Your current blenny will probably get along OK with any goby, If you really wanted to add a second blenny, I would definitely not add a lawnmower like peasofme said (lawnmower blenny while fun are nasty little suckers) or starry blenny (fun too, but I suspect them to be nasty to other blennies too). I would either try a sailfin blenny (like a black or golden) or a venomous blenny of some sort.