What type of paint should I use on my hardwood floor?
If I were you, I'd invest in an oil-based (mineral spirits cleanup) primer. I've painted several old wood pieces of furniture and you need the adhesion to whatever they used on the wood previously. Remember, it's likely in an older house that they used all sorts of older oil stains on the floor and latex has a hard time gripping them. Oil-base primers can overcome that issue.

Once the floor is primed, you should be set to paint whatever product you see fit, latex or otherwise. If you paint latex, be sure to use a water polyurethane as well (which doesn't yellow). You might want the extra protection for the paint. A semi-gloss or hi-gloss paint might not stand up well to the traffic by itself.