I know I purposely keep my house cool in the winter (saves money on the heating bills) so my dogs all keep their coats amazingly well enough they have NO TROUBLE in the coldest weather as long as they are moving. So I've never had jackets on my GSD's on one of them had a really short/sleek coat. In fact they will go up to their bellies in ice cold creeks during a walk and have no problems continuing.
I'd call and discuss with my vet the amount of exercise recommended, not sure what surgery was involved. But generally if he's doing well, then start limping then you can have an idea of what's pushing his limits.
MACH3 Bretta Lee Wildhaus MXG MJG MXF MFB TQX HIT CGC TC
Glory B Wildhaus AX, AXJ, XF
"How is it one careless match can start a forest fire, but it takes a whole box to start a campfire?." ANONYMOUS