Cant see why not a blue gourami, size wise (trying to remember off the top of my head now, been over a year since I had gourami) the blue & gold get between 4-6", had my Rotkeils with them for a while without bother. If you can get hold of them the snakeskin gourami is gorgous but that will get approx 8"+, but if the mrs wants blue have a look at the moonlight gourami, not as blue more silvery blue, very nice but again bigger than the normal blue gourami so may fair better with the red spot severum.
If you want a siamise tiger, forget the rams, tetra & cory's. Beautiful fish, not kept them personally but I had someone come and get some of my Rotkeils, he had a monster tank with only siamese tigers in (showed me loads of pics of all his tanks on his phone, nice chap too) They are aggressive he was telling me and actually stalk and hunt other fish, they will eat anything that they can get in their mouths. He gave up putting other fish in with them so now just has a species only tank with them in.