Rhyb - I probably don't have a great answer for you but here's my thoughts. I think you need to definitely work on yourself - there are so many ways you can do that but I think a lot of it comes with age and experience. There's so many resources out there in areas of self development...it allows you to start looking at the bigger picture of life I believe and not to focus on things like superficial appearance. Also, being aware of what other go through can make you feel very grateful for what you have (even if it's sagging!!) People in wheelchairs, amputees, burn victims...etc Sometimes we all need this reality check to bring us back to what is important. Your body has done some amazing work by providing you with 3 gorgeous children - be PROUD of it! There are plenty of people that would do anything to be in that position...
The most important thing is that you recognise it which is fantastic - just that alone will make it easier to set the right example to your girls.

I also think there needs to be a balance - it is ok to want to look nice, to get dressed up in nice clothes and I think we also need to not go over the top - it is ok for a woman to want to feel sexy or attractive - especially to her husband/partner...I think we just don't want kids jumping into things when they're too young...it's easy to make this backfire and have girls growing up ashamed of themselves as sexual beings...There's a fine line!!! As I've said before, I think it all comes down to being open and honest as kids get older and educating them!!

I hope I haven't rambled on too much...