Like you, my legs and arms tire out very quickly and that could be unsafe if you are
in a
pool with a deep end and are not swimming
in a lane near the edge of the pool. But, let me suggest something that has helped me. Have you thought about using a kick board? It has helped a lot with strengthening my legs. If you get tired, you can just float.
I used to swim at least 40-50 laps before I'd call it a day, but now if I can swim 5-6 I think of that as a good day.