I'd agree about using a floor like Flexitec instead of vinyl tile. It'll save you a lot of headache. It sounds like you have a fair bit of movement in your subfloor if it's cracking again so quickly. I would glue the vinyl down instead of loose laying but that's a matter of preference. Flexitec and similar products are easy to cut and lay for a DIYer but they are quite heavy so bring a friend. All you have to do it cut it in, apply a layer of glue on half the floor with a 1/4" nap foam roller and let haze, lay the floor over it, then peel the other side up and repeat the process. It's also fairly forgiving of imperfect subfloor conditions. You want the floor fairly smooth, but the cracks shouldn't telegraph through like they would with a normal vinyl.