I get how hard it is.
Lack of time, lack of money, and lack of space all make it incredibly challenging to do what you want to do.
Fortunately, I found a way around it.
Back when I competed a professional Muay Thai fighting in Thailand I was faced with not only having to improve my muay thai skills and technique, but having to do so without using weight training exercises.
At the time I was a big, bulky and puffy looking, weighing 210lbs and being terribly out of shape.
Since I had to fight at a weight of 174lbs, using weights or resistance equipment was out of the question.
My Muay Thai trainer was pretty emphatic about this too.
So I had to come up with a solution to improving my overall strength and conditioning while losing weight, improving cardio and getting into fight shape.
This all had to be done quickly and without much time to spare. Working a 9-5 job, caring for my kids, and attending Muay Thai training five days a week left little time left over to train.
I tried everything out there at first, just like you have, but nothing seemed to work.
Then I realized that if I combined the right bodyweight exercises with the right training modalities I could create a plan to use in my garage, in my living room, in the backyard or after my muay thai classes. No commercial gym membership needed.
...Through this plan, I was able to improve my overall strength, conditioning and muay thai performance while staying injury free.