Re: Ulf Stricker here!
This is a very good question.
I would try to combine more than one thing in an exercise for example: Try to play reading exercises over ostinatos to practice reading and coordination at one time. Play rhythmical pyramids over a certain sticking to practice speed, endurance and coordination at one time.
Practice different things each day, for instance one day in the week is the "feel" day for me, where I just play time in as many styles as I can imagine at that day. Another day could be the "tempo" day. Everyone has tempos where he feels uncomfortable, "wanting" to speed up or slow down. Work on this for one hour every week. I have a rudiment workout routine as well, I grab one rudiment and practice literally everything which comes up to my mind with that ver< particular thing: Solofills, Grooves , Coordination Exercises, Permutations and so on
Or: Make a schedule for each week and try to really keep it, i.e. 10 min warmup, 10 min soloing, 10 min some new technical problem, 10 min brushes, 10 min doublebass, 10 min free playing. There is lots of possibilties. The latter is sometimes hard because you feel bad stopping something after 10 min not having achieved your goal, but maybe you reach the goal in two weeks and then it was worth going that extra mile.
I hope some of my ideas can help you a little bit!
Greetings from Germany!