I love mine.
My first advice is visit lots of doctors, and bring pix from topless lady mags (y'know

) so they know what you want to look like in terms of size and shape.
Also prob stick with a board certified plastic surgeon. i visited with a couple of cosmetic surgeons and they were a waste of time, they are not as good. the reasons why are lengthy, you may already know if not i'll explain.
mine are silicone and i've had them over 4 years, they're 350cc. love em so so much. mine are under the muscle. however, b/c you have an issue w/ feeling like you are sagging, you might look better w/ having yours over the muscle.
if over the muscle is a better option for you be happy, it's much quicker healing. generally speaking it only looks better on women w/ sagging breasts, on women that are still taut under is better.
Also imo if a doc wants to go in thru belly button or underarm that is a bad sign. The best doc's still want to go in right under your breast. if you have a great doc, that scar will fade and be practically invisible in 6 mo's, and it's under your breast anyway. The further away they cut from your breast the harder it is for them to place everything even and just right.
if you visit w/ a doctor some are very short in their consultations but some go on and on or have special assistants just for consults and you can get a huge amount of info out of them, bring a notebook.
Also you may want to go big. I'm a 34D and I don't feel big at all, once you get used to them....surprisingly you'll find lot's of women who feel the same.
Price varies according to dr and regionally. Don't pick according to price. My doc wasn't the cheapest I consulted with. Idk about $ because it's been a while, prices may have gone up, plus i had 2 surgeries at once.
Just do tons of research until you feel comfortable.
Keep looking around online, talk to docs.
Best wishes!!!