Wow, a 19" bike would be waaaaay to big for you, how did you manage to ride it? It's no wonder you had some pains. Other than that you seem to be doing everything else correctly. Going to a bike shop(s), getting fitted, trying different bikes, test riding, doing some research.
About the weight of the bike, when you first start the issue will be getting it on and off a car rack, if you plan on doing that. Don't worry about it for riding just yet. Put some miles on it, get used to riding, build a fitness base, then worry about a lighter, different styled bike.
Don't worry about how many miles you can ride on a "comfort bike". You can ride it as far as time allows. The bike doesn’t know, and doesn't care, how far you take it, or what kind of bike it is. My wife and I did an impromptu 35 miles on Sunday. Me on my single speed, her on her comfort bike. It took a little longer than on our road bikes, but we enjoyed every inch.
There is some good advise above about the women specific designs, you may want to look at them. My wife is short, and she has a wsd bike, and it fits her almost perfect, she rides it a lot.
The main thing is to get a bike that you will enjoy riding. If you don't, you won't ride it.
My wife and I ride the D&R from Frenchtown to Lambertville/New Hope a couple times a year. She usually rides her road bike, she likes it that much, and the surface is smooth and hard enough so it's not a problem. It's a nice ride, hope to see you out there.