Could you use a futon mattress instead of a regular mattress (more details)?

I am a college kid moving into my first house. I need to get a mattress but I don't have/want to spend a lot of money. I was thinking of getting a futon mattress from ebay and then putting a 3 inch memory foam pad on top of it. I have never slept on a futon but if I got a higher end one do you think it would work out okay? What futon mattress should I get for this purpose foam or coil? Firm, Medium, or soft? any input would be amazing thanks!