Bit of a mumsy post, but it's not a good idea to wear high heels all the time - it really knackers your knees and is likely to cause bunions. Try sticking to a 3-3.5 inch heel; they're still elegant and give the illusion of height, but are more practical to walk in. If you really feel you need to go higher, try platforms or at least something with a sturdy heel, not a sliver of stiletto.
Personally, I think 2-3 inch kitten heels look the job.
I think wearing 5+ inch heels a lot is mad, and to me at least, they don't look very classy either (don't hate me, just my opinion!!) You also need to be able to walk in them - no one looks sophisticated tottering around on vertiginous heels they're not used to.