I'm with the others here who have found that dancing classes are what has done the most for me as far as being able to wear higher heels and for longer periods. I'm not sure how you would replicate that with foot exercises, though. Maybe if you look online, you could find some foot exercises for heel wearing.
I read once that a heel height is too high for you if, while you have the shoes on, you cannot raise yourself up on your tiptoes an inch above the footbed (this would be impossible to do with booties; you'd have to try it with classic pumps). I have definitely found that if I can't raise my foot up this high, my feet tire much more rapidly in the shoes, and I have more difficulty walking at that heel height. This might be a good way for you to pinpoint which heel height is your maximum. After you get used to a particular heel height, you can go up to the next-higher one. I would go in increments of .5 inch.
It's good to change your heel height daily, to prevent the calf muscle from getting "stuck" at a particular length. I would get yourself a few pairs of heels, in different heel heights and with different surface areas of heel (chunkier heels are easier to walk in). It would also be a good idea to stretch your calves out after wearing the shoes.
I agree that for whatever reason, certain shoes are just more comfortable than others, regardless of the heel height. Unfortunately, it takes a lot of experimentation to find out what works, which usually means some failed purchases. It took me a long time to find out what worked for me, and I still make mistakes! In particular, one interesting thing that I found out was that I normally wear a half size smaller in heels than in flat shoes. I think that the foot spreads less in heels, which would account for the size difference.
