JellyBelly - I had bilateral osteotomies aged 7, so I know what you are going through.
I didn't have Perthes, but inward rotating femurs, that got worse every year, so surgery was the only option of avoiding a wheelchair for life.
I won't lie - it was painful. I remember waking up in a recovery ward with a nurse telling me I wouldn't be able to sit up (Mums not allowed except at visiting times on wards then), and I also remember a HUGE cage of lights over my legs to dry the plaster out. I was in a spica frame from just below armpits to toes.
After cast was removed I had daily aquatherapy to get legs moving and had to re-learn how to walk (I had never had feet pointing forwards before!). I remember progressing from a walking frsame to crutches to sticks to free walking :)
The only problems I get now are muscular - as the bones were re-set in place but the muscles had grown round them in the old position. I can walk perfectly, and could from a few months after the op.
I believe now that the spica frames are more of a knee brace that also lock the hip position - I am 44 and my experience was a long time ago. However, I would do it again as I can walk and would not be able to without it. My Mum says she agonised over her decision, I am eternally grateful that she gave consent.
Best of luck :)