it's probly hard to find much variety in mushrooms if ur shopping at the normal white ppl's grocery store. bellas and buttons are the only choices i've seen. if u have any asian enclaves around u, there will be markets there where u can try a bunch of other mushrooms like oyster, shiitake, king trumpet, enoki, wood ear.. they all have diff textures and tastes so u could experiment to find what u like.
i'd use sweet onions as a raw component. if u think red onions are strong, try cooking it a bit longer, they should taste better imo. and the darker color always makes me hypothesize that its healthier.
and btw, onion/mushroom is a very western pairing to steak. u might think of other veges, but if this is comfy for u, i'd suggest trying oyster sauce with it. go surf n turf

went to the local asian market and bought me up some shiitake mushrooms there deff diffrent lol. but i dont really eat veggies at all lol, accept when i make a steak with mushrooms and onions on it. everyone who has been eating them likes them so it makes me happy lol. i also threw in a little bit of liquid smoke during the last time and gave it an extra little smokey flavor and it was great. ans specific things i should try with the shiitake mushrooms?

around here we have shiitakes and oysters mushrooms in pretty much every groceries/fruit market..
shiitakes should be treated like regular white mushrooms except that you need to remove the stems, they too hard to eat (you could make a broth out of em if you have a lot)