As of last week, I am booting a bzimage+initramfs combination just fine. bzimage will be fine.
It's a good idea to set the command line args, and I recomment, for testing console=ttyS0,115200 earlyprintk=ttyS0,115200,keep
Your best bet is to do the standard trivial initramfs with a simple program: main(){printf("hi\n"); while (1);}
Let's pretend it's called mymain.c cc -o mymain -static mymain.c
put that in your prototype root file system with the name init. make sure you create /dev/console. Then bundle it all up with cpio and you've got an initramfs
I can start some notes on the wiki if you're still stuck.
ron