could try the cross trainer ?? it is low impact on the knees and you still have to stand up straight to do it ? back extensions will help as well with strengthening your back which will in turn help you stay up straight.
Even if you can get 2 massages in a month if youc an swing it financially I highly reccomend that. I know it is pricey costs me 80 bucks for 45 mins but so lucky as my work covers it on our health plan