By electric yellow, do you mean Labidochromis caeruleus?
You can get pretty much any Mbuna and add them together as far as I know. I've only had Mbunas for a few years now so my knowledge is very limited still.
I don't agree with many compatability charts because they never seem to hold true for me.
There are 3 main aggressive Mbunas-
Melanochromis chipokae (I would stay away from this one just to make it easier at the start)
Melanochromis auratus
Pseudotropheus lombardoi
Most Mbuna are aggressive and they can take care of themselves, so don't let that scare you at all. I am only naming the 3 I've had real problems with, and the only one I couldn't ever get to settle down was the chipokae, but others have had better luck, so you might also if you want to give it a try.
I would get socolofi, Ps. zebra, lombardoi (kenyi), johanni, among more.
Try to get different colors and sizes if possible (I know that's hard if bought at a young age), and try to only get 1 male per breed. You can get 2-3 females of the same kind and it should be ok.
You can put quite a few in a 55. (I think that's what you said you had?) I've heard of people having 25-30 of them in that size tank. I don't want to say whether I recommend that because I haven't ever seen it or tried that, so take that for what it is.
What type of filtration will you have?
Get a lot of rockwork in there as they love rocks. Mbuna means Rockfish.