http://www.cheapair.com/blog/travel...-overweight-passengers-traveling-this-summer/
Domestic Airlines (written April 2013)
Southwest Airlines:
Passengers who cannot fit into a seat must purchase an extra seat, either online or over the phone, although they offer cheaper rates over the phone for the extra seat. Southwest also advises that a passenger of size may contact them for a refund of the cost of additional seating after travel.
Passengers of size who do not purchase an additional seat in advance have the option of purchasing just one seat and then discussing their seating needs with the Customer Service Agent at their departure gate. If it is determined that a second (or third) seat is needed, passengers will be accommodated with a complimentary additional seat(s). However, you may be bumped to another flight if no extra seating is available. Southwest Airlines’ width between armrests measures 17 inches.
American Airlines:
American Airlines requires passengers to purchase an additional seat or upgrade if they do not meet one of the following criteria:
Unable to fit into a single seat in their ticketed cabin and/orUnable to properly buckle their seatbelt using a single seatbelt extender (available upon request from a flight attendant) and/orUnable to lower both armrests without encroaching upon the adjacent seating space or another passenger.
American Airlines notes passengers to address their seating needs at the time of booking the original reservation. If seats are available in your ticketed cabin, you may be accommodated in the same cabin next to an empty seat. The additional seating must be available without downgrading or unseating another passenger. If time allows, and upon payment of the fare difference, you may be offered a seat in a higher class of service that may provide more space. If additional seating is not available, passengers may purchase a second adjacent seat on a different flight. The fare for the second seat will be the same as the original seat. American Airlines economy seat width ranges from 17 to 18 inches.
United Airlines:
Passengers traveling on United Airlines are required to purchase an additional seat or upgrade if they do not meet one of the following criteria:
The passenger must be able to properly attach, buckle and wear the seat belt, with one extension if necessary, whenever the seat belt sign is illuminated or as instructed by a crew member.The passenger must be able to remain seated with the seat armrest(s) down for the entirety of the flight.The passenger must not significantly encroach upon the adjacent seating space.
United will not board a passenger who declines to purchase a ticket for an additional seat or upgrade for each leg of their itinerary when required. The second seat may be purchased for the same fare as the original seat, provided it is purchased at the same time. A passenger who does not purchase an extra seat in advance may be required to do so on the day of departure for the fare level available on the day of departure. The passenger may instead choose to purchase a ticket for United First, United Business or United BusinessFirst, or elect to pay for an upgrade to a premium cabin if there is availability to do so. United Airlines economy seat width ranges from 17 to 18.3 inches.
Delta Airlines:
Delta does not require passengers who need a seat belt extender or are unable to lower the armrest to purchase additional seats. However, you may be asked to move to another location that provides additional space. In the event of a full flight you will be asked to take a later flight with available seating. To avoid this, Delta Airlines recommends that you purchase an additional seat. Economy seat width is 17.2 inches.
JetBlue Airways:
No clear policy is stated online. When calling Jetblue, they advised to either purchase an additional seat at the current price or opt for a seat belt extender. JetBlue seat belts are 45 inches in length and you can request 25 inch extensions on-board the aircraft. Economy seat width ranges from 17.8 to 18.25 inches. Passenger’s who cannot fit, will have to purchase an extra seat at the current fare offered.
Spirit Air:
No policy is published online. When calling Spirit Airlines, they will advise you to either purchase an additional seat at the same cost of the first seat, or to purchase a Big Front Seat which offers additional seat width. Economy seat width is 17.8 inches. Spirit Airlines offers Big Front Seats which is 18.5 inches wide.
While we wish there was a standard industry wide policy, the reality is that each airline handles overweight travelers differently. International carriers are no exception. For example, in Canada, forcing one passenger to buy two seats is illegal on domestic flights, because Canada’s Supreme Court ruled that charging extra to someone who is “functionally disabled by obesity” is discriminatory.
To book an extra seat for yourself you will need to call and speak with a travel advisor who can assist you since each airline’s policy is different.
I just bought our tickets today, they finally extended the dates of availability. I got 3 seats to have the extra width and the upgrade for leg room. Sounds like it will be similar to First Class without the price. I have been looking at flights for months and LAX to BOS is about $2500 for First Class. I spent $1500 for 3 seats, a BIG bargain, non stop, YAY. 
I notice you are from New England, are you familiar with Boston?? If so, what kind of tour would you recommend for Pooh??? We are flying in the day before a 14 day cruise and would like to do a tour the day we return since our flight home doesn't leave until 7pm. 
