I use vivariums for all my hedgehogs - they come with air vents which allow for air circulation, so when looking for one, make sure they have them - the VivExotic range are good and I have had no problem at all.
Even though your room may be warm it still may not be warm enough for your hedgehog - you can either use a Ceramic Heat Emitter and Controller or a heat mat - I use both but mainly the heat mats, I put half under their sleeping area and the rest is out in the viv - I have not had any hibernation attempts and to be honest, unless we have a heat wave, my mats stay on 24/7 all year.
You need to get a minimum of 3ft in length but if you have the space for a 4ft they go for this size as your hedgehog will appreciate the extra room.
Check out the stickies in each section as there are some good tips in each one and if you need anything else, just shout out xx