There are a few things to check...the bottom bracket cups need a little grease on the threads, which will help prevent creaking. If they are not tight enough, that could cause creaking as well.
Also check the pedals for play and make sure they are snug, it could be that simple.
I dont think the bottom bracket is at fault here, probably just the threads in the frame and on the BB cups that are creaking. Normal bike grease or marine bearing grease would be fine. I use Park polylube 1000, I bought the 1lb tub, more $ than marine grease but I like it and It should last me a LONG time...