I travel solo alot, not just Disney but all over Europe and on my USA vacations. I don't use travel companies and book all my hotels, transportation etc myself. As PP have said most travel companies add on a single supplement , which in my view puts me off using them. If you like the look of the New York Trip, why not do it DIY.
For flights I use a comparison website called SKYSCANNER
There are lots of online hotel broker websites. These are websites who block book hotel rooms and then sell them cheap. I have used Expedia, RoomX and Opodo but Im sure there are alot more. The rooms are cheaper than booking direct with hotels BUT you usually pay in advance and there is no cancellation refund
Other than the broker websites, I also just go to Google maps of a city I want to visit, zoom in on an area, for example Mid Town Manhattan and see what hotels show up. You can then go to the hotel website and check out their rates and availability.
For things to do and see, most cites have very good tourist information websites which I use as a starting point. One thing I do in every city I visit is take a hop on hop off bus tour, so if I'm researching a city, I will find the company that operates in that city. By checking out the hop on hop off bus routes you also find most of the tourist must do things, like museums, places of interest, local history etc.
I am a Hard Rock cafe fan so, again if I am researching a city I will see if they have a Hard Rock Cafe and where it is.
It actually very easy to do a DIY vacation and the best thing is is usually works out cheaper than booking through a company