If the heat lamp is working fine on achieving the required temperatures, definately the cool hide. Please make sure it is not a half log... as we all know, they make BPs feel very insecure. I recommend the hides from reptilebasics.com they are very good.

http://reptilebasics.com/Hide-Boxes-p-1-c-282.html

If you cannot get two of those hides, try to get a similar/exact hide for the cool end. The same hide on either side makes sure the snake does not favor one side more than another because it feels more secure on that side.