There is no definitive benchmark on success. It is entirely subjective.
Happiness might be a gauge but, as you know, that goes up and down quicker than you can keep track of it.
Other people might define how well you're doing, but the quickest way to get anxious and miserable is to judge yourself against others – so that's no good as a gauge either.
Without a benchmark, you can look at your well-being in two ways:
1. You've not done enough, nothing is good enough, and you'll never quite be enough.
2. Everything you do from this moment forward is a bonus – a bonus on top of everything you've already done.
When you choose #2, you stop beating yourself up. It gives you a sense of relaxation and freedom. It allows you to live in the moment. And you should choose #2. With all the problems and challenges you have faced, you're already an over-achiever.