August is not the busiest time in Orlando / at WDW at all. Christmas, Easter, July-very early Aug, 'Spring Break' and sometimes the Labor Day weekend in early Sept can be busy, but the last 2-3 weeks of August tends to be less manic, as American schools go back in early Aug (although very, very hot and sometimes stormy).
I know there are some horror stories above, but I honestly think it is do-able if you can swallow the price of flights (pricey all year round and extortionate during school holidays - no getting away from that). Disney / Orlando really can be a lovely holiday.
For accommodation: Look on owners direct website. We have hired a lovely 4 bed villa with own pool in Kissimmee (about 20 min drive from Disney) for £500 a week. If you are willing to stay in an apartment block and to go a bit further out than I-Drive / Disney (so out to Lake Buena Vista, Kissimmee etc) you can probably get something cheaper.
Disney hotels are a rip-off and not great quality, imo. If you hire a car, it makes much more sense to stay slightly further out, somewhere with a pool for 'down days', and drive in for all the excitement of Disney / Universal etc.
Disney and Universal both issued 'fast passes' for my son, who has SN, and I am pretty sure if you call ahead and explain the situation with your DH they might also do the same for you. It means you can 'book' a slot on a ride and not queue for hours (still have a 15 min-ish wait, though).
Having said all this, Orlando isn't really a laid back beach holiday. You can get relaxation by the pool or at the water parks, and you can drive out to lovely beaches if you are willing to do 2 hour-ish drives (and swim with Dolphins at the lovely Discovery Cove - but pricey!) but most of the fun stuff is quite active and full on, and in the heat it can be tiring for even the fittest body!