Hey Hanna,
For once, Petsmart is right! Two oscars would not be happy in a 36 gallon. That's too small for just one oscar. A full-grown oscar can be more than a foot long and they are active, intelligent fish. If you don't keep them in a nice large tank (like 100 gallons) with things to keep them occupied, they have a reputation for dismantling your filter or your heater because they are bored. I don't know if you've noticed, but at the fish store they all swim right up to the glass if you stop in front of their tank, because they are curious about you.
You could fit a pair of dwarf gouramis in your tank, along with say 6 barbs, rasboras, or other small fish that like similar water temperature. Check the fish profiles for details about the gouramis, and then look to see what is compatible. Remember that while the gouramis are happy as a pair, small schooling fish generally like to be in a group of 6 or more, so you would need to use SMALL schooling fish, so that you would have room for enough of one species for them to be happy. Look at the fish profiles. Also, although dwarf gouramis are generally thought of as peaceful fish, we had a heck of a time finding a pair that would tolerate each other in our tanks. Fortunately we had three tanks going at the time. I think we ended up with one gourami in each, because they were bullying each other.
If you want to try some ciclids, you could put a pair of kribs in your tank with a small school of smaller fish. Again, look at the "fish profiles" section for the kribs. See what kind of water temperature and environment they prefer, and then find a small schooling fish that likes the same conditions. Again, just add one other type of fish so that you can keep them in a large enough group for them to be happy.