You certainly aren't a dummy, nor are you alone. I doubt any fish hobbyist can say they didn't have the wrong species in the wrong tank with the wrong other species at some early point in their hobby. I once had a baby Angelfish (should be in a 20 gallon, minimum) with a baby common pleco (get 12-18 inches- need 55 gallon or better) and three serpae tetras (should be in groups of 6+ in 10-15 gallon minimum) all together in a FIVE GALLON TANK. Duh.....
Anyhow, I'm sure if you post a picture someone can identify your fish and give you an idea of it's requirements before you take on more than you really want to. You might also describe your present tank and why it's so difficult to clean, chances are there are ways to make it easier.
I think you are more stressed than your little fish! Buy him/her some frozen brine shrimp or bloodworms for a treat until you decide what to do- fish live to eat, the little guy will love you for it. (In fact, the fish may be visiting the corner you found his deceased "buddy" in for an entirely different reason- it may have started munching on the body and is still looking for his snack bar... fish are fairly practical in matters of life and death.)