I think you should do some cardio and some weights, as strength training is also beneficial for general wellbeing and lots of other stuff even if you don’t aim to get buff.
Cardio: personally I hate running on treadmills, I like to be outside and find it easier (more stuff to look at and air to get rid of your sweat). But try whatever they have and see what you like. Rowing machines are good because they use all your big muscle groups, or on an elliptical machine or stationary bike you might be able to watch something at the same time. Start easy until your in the habit, then look into intervals and higher intensity stuff.
Weights: I find it easier to use free weights like dumbells if they have them, but the machines can be good too. Find exercises that use your big muscle groups like squats, benchpress, rows. Don’t bother with fiddly machines that isolate one random tiny muscle. Start with low weights, but ideally work towards finding a weight where you can do 3 sets of 8-10 reps, with a 2 min rest between each set. By the end of the last set you should be pretty much not able to do one more rep (but that’s just for best results, not absolutely necessary).
I also find if it’s possible after you work out (and after shower if you’re doing that right away) try to take 5 mins just to sit/lie down and be aware of how nice and tingly your body feels. Really tune in to those endorphins making you feel nice, that helps me come back next time, so you don’t just remember the hard bit.
Arschubervollmitseifgefuhl, The feeling that you have too many bars of soap up your bum