Configuring the prefix key to C-z is quite harmless, C-z C-z for suspend is quite ok.
(As a bonus hint, binding subkeys with control it's faster to send commands: C-z C-n is faster than C-z n, you just keep control pressed during the command sequence.)
Of course, it's easy to fix. It just boggles my mind that they would have made that mistake in tmux to begin with when you consider that it's one of the main complaints people have about screen and tmux was supposed to be a "better screen".
(As a bonus hint, binding subkeys with control it's faster to send commands: C-z C-n is faster than C-z n, you just keep control pressed during the command sequence.)