What about ordering an air mattress from
Walmart? They are about $8, then throw in delivery fees and the resort's package fees.
Alternatively, ask the resort for a mattress topper for the sofabed. When we requested this from Saratoga Springs, they arrived in two pieces that we pieced together and covered with a bedsheet. One adult could take the topper and place it on the ground as a "mattress". The topper is very thick and should be quite comfortable enough (I have done this for camping).
And yes, I have been the family to give the master to one adult traveling with a party of 8. We were a group of:
- DH and myself (paying for the bulk of trip)
- my DD16
- my DS14 (he's about 5'4)
- my brother, SIL, and their 3 yr old
- my father (who also contributed a little towards the trip)
I absolutely did not want my father on the sofabed (although he offered) and it just wasn't comfortable for anyone to share a room with him. So we divvied up like this:
Living room - DH and myself on the sofabed, DS14 had an air mattress but was comfortable with two sofa cushions pushed together to make a mattress (I had brought a fitted sheet) so we didn't bother to blow up the air mattress
Studio with 2 beds - my brother and SIL, my 3yr old niece and my DD16 on the other bed
Master suite - my father
We were there for 2 weeks and my father was only there for one week though. So DH and I took the master suite the rest of the time and my two teens slept in the living room. I did think about giving my SIL the master suite so we could have the living room as common space - but frankly, we liked sleeping separate from our teens so insisted our teens have the living room.
That said, DH and I were comfortable in the living room

I know SSR has a tight living room, but there was sufficient space for all of us and we left the sofabed unfolded and DS's makeshift bed out the entire time. Our only complaint is the complete lack of any type of closet space in the common living areas of a 2 bedroom villa in SSR.