Hi and welcome to the Disboards.
I assume you've got a similar problem that I do. You'd like to get 2 double beds instead of the kingsized one and still have a roll in shower. This can be done depending on the resort.
I stayed at Port Orleans Riverside last week and they do have rooms with roll in showers and 2 double beds. I do know that the Wilderness Lodge only has king sized beds in thier "wheelchair accesable" rooms. So it really depends on the resort. If you talk to the people who handle medical reservation requests they might be able to recommend a resort that can accomidate your needs.
Another thing to consider is whether the accesable room is what you need or if you just would like one closer to the loby, food court etc. I've been a paraplegic for 26 years and the only time I've ever used a roll in shower is at WDW. Personally I hate them. I'd much rather have a room with a tub. The only reason I request a accesable room is because I travel with my daughter and I need to close off the bathroom door behind me. Since my daughter is 19 now I'm thinking of planning a solo trip and when I do I'll take a normal room with a tub. I was speaking to a CM last week about how the doors in the Disney Vacation Club model were all large and I liked it, he said it was now required by Florida law. So I bet anything new or refurbished will have large enough doors so that I won't need a roll in shower room.
If you feel comfortable giving abit more information, like number of people traveling and the limitations for your child we might be able to recommend a place that will work out well for you. Hopefully you'll have a great trip wherever you end up.