Last opposition, I could see dark shapes and the polar cap in a 6" scope, so all you need is a night of decent seeing. The great thing about Mars is the day is slightly longer than ours so if you get the chance to see it on successive nights you can see different faces
According to sky safari, Mars is only 6.8" now but will be 15.1" at opposition. Not the best, but as it'll be huh in the sky I hope we still get to see some good stuff. Only a shame we don't pass each other by more often IMO.