I have ridden a bike all my life, even after having both knees replaced. But I fell a couple of times last year and pulled some tendons and broke loose some scar tissue on my right knee. Instead of riding 7-8 miles easily, I could ride 2 miles and then not be able to walk the next day--not a good situation.
Here is the bike I have:
http://www.eco-wheelz.com/catalog/eg-at ... -p-357.phpOne thing I like about it is that it has a very low step-over, so I can get on or off easily. What I don't like is the weight. I have twice fallen very slowly because once it starts to fall, it is so heavy it is hard to get it back upright. It weighs 54 pound with the battery and about 45 pounds without it. I take the battery off before I lift it on the bike rack, then cover the whole thing up. The battery lives in the motorhome to keep it dry and to recharge.
I do love the pedal boost feature and the lithium ion battery. If you are looking at electric bikes, you really want to avoid the lead acid battery versions sold more cheaply. These batteries are good for only about 100 charges and then wear down. The lithium ion battery charges faster and lasts longer.
I am short and this bike fits me well. I bought a set of panniers that were made for this bike and they fit on very nicely, plus have a laptop sleeve, as well.