I think everyone has their "favorite" exercise method, even if they hate exercise ... or hated it before getting into the habit of it. Therefore, let me preface this by saying that you're obviously going to have to find something that you are able to do as well as something you at least enjoy a little bit, otherwise you're doomed to failure.
I imagine you'll get a lot of people telling you to just get out and walk, which is fine. Walking is great and I don't knock it, and I know it's worked great for many people ... it's just that it's never worked FOR ME. I have found walking for exercise to be frustrating and boring, and I would rather walk for enjoyment with exercise being the side benefit! When my youngest daughter was a baby, I went through a period of low-fat eating and walking all over the place, and my fitness/weight didn't improve at all. In fact, I started getting bad pains in my heels. I, too, was around 100# overweight -- no, actually it was a bit more than that ...
What I'm doing now -- and again, I was to emphasize that this may not be for you -- is lifting weights. I've been making it a concentrated effort for about 10 weeks now, and I'm feeling great! Last spring, I had pains in my joints and often in my back -- I can't say every little pain is completely gone, but they are significantly improved. I don't wake up all "creaky." While I know that aerobic exercise is important, I'm not doing as much as is "recommended" right now and you know what? That's okay! At least I'm moving. And I know that once I drop some more weight and feel stronger, I'll enjoy doing the aerobics more.
Here are my perceived benefits of weight-lifting: (1) from my very first work-out, I felt a nice little burst of energy - and I continue to feel good after each workout - I'm not a big fireball of energy, but I definitely have more energy during my day than I used to; (2) I'm building muscles and making myself strong, and I can feel this quite definitively; (3) building muscle helps to raise your metabolism, which in turn burns more fat; (4) I have a much better attitude - no sinking into helpless depression, which is something I've struggled with for a long time; (5) I can do a routine at home or at the gym; (6) I truly feel I'm progressing faster with my fitness than if I were just walking (see what happened the last time I tried that).
You can start with very low weights, or even no weights at all. If you can afford it, you could consult with a personal trainer, or possibly you could work out getting a physical therapist in association with your disabilities.
Another option for you might be something involving water, swimming or water aerobics.
Anyway, I was around 250# when I started all this, and through weight lifting, some aerobics (never more than 15-30 minutes at a time!) and low-carb eating, I've lost about 25 pounds. But even more than that, I FEEL so much better, which primes me for keeping it up -- and THAT's what's most important to me.