I always figured surgery is the only way to lose excess skin, but I've recently heard of two ways to help skin tighten up.
Wearing snug, supportive foundations day and night is said by at least some women to allow the skin to lose some of that stretch.
Supposed to work for breasts, belly, and thighs. I suspect that individual results would vary a great deal, but might be worth trying.
And colored light therapy also gives real results – I was given this info by a former nurse who had worked for a dermatologist. Red and yellow light treatments help produce collagen, which tightens skin. My acquaintance had only seen the results on faces, but found the improvement impressive, and she had heard of good results on other areas as well. It also helps correct sun damage to skin. Tummies? I haven't heard.
But one other option is to accept it. If the majority of women eventually get these natural indicators of a rich life removed, then those of us who don't have the resources to do so will seem less attractive in comparison. It can happen – it already has with many forms of "beautification." Honestly, your tummy got stretched out in the process of bringing (a) new human(s) into the world. Be proud!
I think women do these things out of shame as much as vanity. It takes some deep thougtht and attention, but it is possible to ditch most of that shame and love ourselves as we are. I notice that even though my figure hasn't been ideal since menopause, my dear husband seems to love me just as I am. I'm still working on it, but getting there.