Finding the right size bicycle
A cruiser-style, semi-recumbent trike might be the best for you. 

You can lean back so your stomach isn't in the way. Your back is supported so all your weight isn't on your rear end. Two wheels in the back spread the weight and result in fewer rear tire punctures. The trike ensures that when you're stopped or riding really slowly (e.g., uphill), you won't lose balance. It's impossible to do an end-over going downhill. 

Because it's not fully recumbent, it's still easy to get in and out of, and you're higher off the ground so it doesn't feel as invisible to cars. Steering is done with the usual handlebars so it's easy to get used to. It's easy to move the seat forward for shorter or longer legs and the steering column can also tilt back.

Add an electric assist to the front wheel and you'd be in heaven.