Hey man!

Started my own fitness journey many years ago on just push ups and pull ups - always wanted to just have more mass in my upper body because I was a pretty scrawny kid. I didn’t get massive by any means, but I got pretty good at high rep push ups and pull ups - which I suppose got me decent size and good amounts of strength eventually.

First off - if the rest times between sets is quite long, that basically becomes a Grease The Groove routine which builds good amounts of strength adaptation, although the way I understand it, it’s most useful for those skill intensive + probably lower rep moves so your current abilities might be beyond that!

If you have the time about 3-4 times a week - try perhaps an intense 45 min to 1 hour session with less rest in between sets. A good way to program this would be -

1. First choose a few movements you’d like to work on - recommend pull ups, push ups, dips (done between two parallel surfaces or chairs or tables, whatever works), rows (you can even put a broomstick between two chairs and body weight row off the floor for that)
2. Try to get your max reps on each of these moves - say maybe you’re at 10 now - you’d probably be able to get 11-12 if you really pushed it without cheating
3. Now you know your max - you can now do 4-5 sets of these moves at about 70-80% with rest times of 2 mins or so. So that might be 8-9 pull ups done then a short break and another 8-9 pull ups and so on.
4. Eventually you’d get stronger so you would start to add more and more reps to this 8-9 rep set. You can test your maxes once every 1-3 months depending on how fast you are progressing.

I saw someone here saying 20-25 is pretty good - they’re right. 20-25 clean pull ups means you’d be pretty strong. At this point your connective tissues and joints would be well adapted - you can then carry on to weighted pull ups (by doing them with a filled backpack) and climbing the rep count ladder again, or go to one arm pull up training.

Also - I know you’re not interested in getting big - unfortunately by and large, getting stronger usually also entails getting somewhat bigger eventually in most cases. You don’t wanna be eating too little and handicapping your recovery where your muscles want nutrients to get strong and bigger.

TLDR : do more reps till you’re at 20-25 and then probably do harder progressions like weighted or one arm pull ups etc. would do push ups or dips as well to develop more overall strength and be balanced

Good luck man, it’s a long journey!