I'm happy. It's a mixture of things IME.
Job - on maternity leave at the moment, v lucky to have the option of this up to 3 years in the country I'm in. I'm in the second year, will go back at some point this year or at the end of it. When I'm not on ML I teach ESL, which I enjoy, but dislike my employers and some of the management at the school and the commuting (public transport - I can't drive, which is something that gets me down sometimes.)
Family - I have a genuinely fantastic supportive kind husband which I think makes a huge amount of difference to my happiness day to day. Just having someone there who has your back is invaluable. Also a million times better than my previous relationship (DS1's dad) which was emotionally abusive/controlling/generally miserable and shit. Also have an 11yo who I feel I'm failing constantly and worry about a lot but then on other days am hugely proud of and so I have no idea where I am with him any of the time - err bring on adolescence, because I have a feeling it might be a rollercoaster. And a 16mo, who took us years to have and also is in one of my favourite parenting stages ever (1-3 years) so is just adorably hilarious pretty much all of the time and I don't feel lost with him at all because this phase is easy and I feel confident in handling it.
Money - I keep thinking we are well paid although actually having looked at averages, not as well as I thought - I was thinking of a very outdated average figure. German average is higher and we are well below that but still second quartile, I think. But definitely don't feel rich and tend to have to scrape together pennies due to some silly debts which swallow up over 1/3 of our income. However, have recently made a plan to get this down which should help. Money is a stress, but I have this nagging sense that it shouldn't be.
Health - Physically am all good. Have ADHD which I struggle with sometimes, but it's much better managed now than in the past, which makes a big difference. DH worse than me for health with two injuries/longterm health issues but they don't get him down unless they are really flaring up. Or possibly they do but he doesn't mention it.
Attitude - Maybe. I have definitely had some shifts in thinking which have made a huge difference to my mental health/happiness. If I think back to times I felt very low the overriding feeling was being stuck/unable to get out of a situation/that something wasn't changing/that things were out of my control or inaccessible to me. Something that has changed this pattern for me is starting to look at things I'm unhappy about and work out what would need to change for that to improve and then figuring out how to get there and then starting to do it, even if it's baby steps at a time. For example several years ago I had the sense that we would just always be poor. Now we are not poor (not rich, either) and I can see a way towards even more strides in our income in the future e.g. me retraining or working in various areas and it makes me feel less hopeless about it. Also years ago when I was feeling in a very stuck place with DC1 vs now where I am able to look into and investigate ideas I have about how I can best help/support him. Yes this is contributing to a horrible sense of why on Earth did I put up with things as they were and not look into this earlier - but at the same time, better late than never and it is helping.
Things I think that contribute the most to my happiness are support - physical/mental/emotional - I was not happy when I was burnt out because I didn't have this. For me that mainly comes in the form of a partner but I do also have a pretty awesome friendship network locally, and the set up in Germany in terms of childcare is also really, really good so that helps a lot too in terms of reducing some of the childcare burden which is a lot, IME.
Then also connection. I realised recently that I tend to bury myself in what I think of as "online reality" rather than face reality which is a hangover from the old abusive relationship, I think. My mental health and general happiness and sense of wellbeing suffers when I do this too much, because my life now is not something I need to escape from. But because it's a habit it's something I have to be quite conscious about. I feel better when I feel connected with the real world, whether that means making social contact with people or just spending time in my house doing whatever to improve the space or appreciating nature (and I have to admit the area we live is beautiful and this is a huge bonus) or that process I mentioned before of making plans for the future and having that sense that I am in control of my life and I can do things that are hard or even seem impossible.
Lastly there is another feeling I can't really put a name to, probably self worth is the best way to put it - feeling that I am accomplished (or at least competent) at things, that people like me, that I am doing OK/not a failure, and so on. So I prioritise spending time with people who seem to actually like me, and I let old friendships/relationships lapse if they served to drag me down. The same making-progress-however-slow thing helps a lot with this as well. Getting actual help with issues which are bothering/hindering me. I'm a long way off perfect but I'm not aiming for that any more, which helps a lot too.