Any clematis in particular that grow well on mailboxes? I really have no idea what a suitable height would be. My favorites are the blue/purple blooms or pink blooms!
Pink Fantasy and Piilu both are pink and stay fairly short for me. I grow Niobe next to mine (it is red), and it does very well and takes all day sun/heat surprisingly well. They can be lightly pruned to stay the right hight too.