Should I get a lift? I'm 19 and had a kid.?

I had a consultation and they said I should wait if I plan on having any more kids. Personally I can afford it. The issue is this is something that has me down. I decided to feed. So losing 30 pounds and feeding for 1 year did bad things. Luckily I dont care about my stretch marks but... my they sag. I have a bf of 1 year an hes 19... of course he wants kids in the future. I'm so self conscious and he's never seen my because I hate them. What should I do, yes i know its my decision but i would like opinions. Everything else on my body if fine accept this.