With a bit of practice, you too can master counting. It's a little tricky at first, but just start small.
Try starting with a number like 4, for example. Go 4, 3, 2, 1, 2, 3, 4, 3, 2, 1, 2, 3, 4. Repeat that until you get the hang of the numbers then move onto larger numbers like 10 or 110.
Then, after all that practice, you can easily just think for a minute. "hmm my sequence is a bit too fast, it needs to be slower..." and figure out what to type into the BPM box. "It's 110 and that's slightly too fast so let's try ummmmmmm 109"
it'll be a pain to keep the numbers straight in perfect descending/ascending order, but I believe in you.
the issue with adding 2 extra buttons to the tool bar is that they would take up too much of the already limited space. you don't really need to change the bpm that much while you're making a song and i think it would just be over all more efficient to type in the current bpm -/+ 1 into the bpm input