So today I bought some high heels, the first I have had in ages, about 4 inches high or so. They feel very burny under the ball of the foot, even with gel pads in. Will wearing them at home a lot toughen up my feet so I don't notice it so much?
Rather than gel pads under the ball of the foot you are better off looking for supports that go under the arch of the foot. Gel pads under the ball of the foot are doing nothing to take the pressure off the ball, and therefore nothing to reduce pain. You want to distribute the weight more evenly, hence the arch supports.
Some heels have better arch support than others, which is why some are more comfortable. I know that I used to wear a pair of 6 inch shoes which were comfy for hours, but then change to a pair of 3 inch heels which hurt after about 30 mins.
You unfortunately wont get used to carrying your whole weight on the ball of your feet.