Thank God you are doing well! I have had some (not as severe as yours) traumatic events on horseback, two this year alone..
So, the 1st thing I would have to advise (within my conscience and common sense, anyway)to follow your Physicians advice..
Having said that, and I am NO Physician either, here's what I can add..
IF NO-ONE can TALK YOU OUT OF IT, period, then obviously safety in all forms is in order here.
You should NOT ride AT ALL for quite a while longer...your healing process isn't near finished...
Next, when you INSIST you must get back,A safe horse (may not be yours for now) is a MUST..A Controlled environment (indoor ring, or well cared for and fenced-in outside ring/area) Walking gaits only for a while (any trotting will be a very bad idea) and ride with visual and audible supervision (better known as a friend with a cell-phone!)
Safety equipment? Certainly a C-COLLAR (cervical restraint collar..you know what that is for sure) A HELMET also..
DO NOT GROUND MOUNT, or MOUNT WITHOUT ASSISTANCE...too risky right now
I cannot condone risking another injury, one that may be FAR worse than you have now, but I know I would be tempted eventually...1st give yourself time to heal a bit more eh?
IF YOU MUST RIDE...pad your odds at all costs!
PLEASE go easy and be careful! -Lw