With your balance and mounting issues, may I suggest that you consider a recumbent trike? 'Most any of the trikes on the market would solve your problems. To start, Sun makes a relatively affordable one that is loved buy those who ride it ( http://www.easyracers.com/ez_3.htm ).

I haven't tried a trike (yet) because I hear they are a blast to ride, faster than they look (though you won't win any races), and highly addictive. If I try one, I'll probably buy it, and I can't afford another bike.

A lot of people tour on trikes, too.

BTW, I won't be hurt if you get something else, this is just a suggestion.