We rarely get prosthetics for people with SCI with leg amputations as it is very difficult to manage skin issues, and because in the USA most insurances will not cover cosmetic prostheses that are not functional.

A customized seating (cushion) system is what you need. Does not wound like you got very good rehab if you were never seated at 90 degrees the whole time you were there. Any chance of going back to a better rehab center as an inpatient to work on this?? 6 months is a very long time to have to be in a halo. The usual is 3 months at the most. I assume you did not have any surgery on your spine for stabilization???