I could be you OP, mid 30's, worked in HR for quite a few years, realised I hated it and wanted out. I went into it thinking I was going to help people, but it was just a load of corporate box ticking bullsh!t, and management who didn't really care enough to make any actual changes. I thought it was just the first company I was with, but after moving a few times, including to a non profit, it was all very similar. The pay and benefits were good, the colleagues were nice, but the actual day to day work just wore away at me.
I eventually moved to a Learning and Development role (which might be an option for you if you want a sideways move), which was a little better but found that I was sick of corporate work in general. Like you I thought if I'm going to be doing this for another 30 odd years I want to do something I feel is worthwhile.
Anyway I am now retraining, doing a course in Animal Care with a view to becoming a Veterinary Nurse. I know the hours will be long and the pay will not be as good, and there isn't much scope for career development. But I'm ok with that. I don't have a family to support so I can take the chance.
Maybe have a think about whether you want to do something office based, classroom based or outside? Do you want hands on physical/ practical job, or lab/research, do you want to work on your own or in a team? Thinking about these might help you narrow it down.
Also you could try volunteering, or shadowing someone in a role you think you might like just to see if the reality lives up to expectations.
Good luck!