You shouldn't need *great* strength for any bike, except to pick it up and carry it. If you know you'll need to do that often, just don't buy a bike you can't pick up. Otherwise, you won't use the bike.

Dutch bikes or city bikes tend to have a very upright posture. A properly set up touring bike also can be quite upright. Hybrids also. An older style mountain bike can be pretty upright, if you look at used bikes. A step through frame tends to be heavier than a "men's" style frame, but is probably easier if your balance is off.

A budget of $500 (in the US) should let you get a useful new upright bike and the basic accessories. Kickstand, lights, maybe a rack or basket, a water bottle cage or two, fenders... If you're lucky enough to live in a city with a bike shop that sells used bikes, you may be able to do better. You'll use your bike more if it's set up to make it easy to ride .

The big thing is to get to a shop and try bikes. Try lots and lots of bikes, even ones that are "too expensive". Some will be ok, some won't. Then you'll have a much clearer idea of which bike you want.