I had the same kind of Sub-floor put in for my beauty shop, I to used peel and stick tile. I primed the 3/4 inch plywood, let it dry. Follow the peel and stick directions for placement. My tiles never came up. You don't need the fancy stuff in the previous reply. I had traffic on my floor for eight years and it looked fantastic till the day we moved out of the home., OH...just make sure to use screws to fasten plywood, we had a floor come up because of nails used by flooring people. Have fun!

First off, if your existing resilient floor is not glued down, then it needs to be removed and the slab properly prepared to receive new resilient tile, so you need to check this first thing you do to make sure it is glued down. Secondly, to go over it, it needs to be down firm and solid everywhere. Any looseness, curling, or bubbles need to be cut out and patched with a cement based floor patch or leveler. Thirdly, if the existing resilient has an embossed pattern, then that needs filled as well with an embossing leveler or portland cement based floor patch or leveler. Everything must be smooth when you glide your palm over the floor, as resilient tile will telegraph any floor inconsistencies through the new product and will become visible over time, so you often have to patch/fill, scrape high spots and/or sand, shop-vac or sweep clean, and repeat until it is all smooth as a sheet of glass. Now, if you have to remove the existing resileint floor if it is not glued down you do the very same thing patching the concrete substrate as you did with the existing resilinet i just explained, if needed, except of course you have no embossed pattern to fill in. I can not express to you enough how important proper preparation is to the looks and performance of your new resilient tile floor. You mentioned slab, so I am taking for granted you mean a concrete slab. Wood underlayments can not be used for resilient instalaltion over a concrete slab. If you did not mean a concrete slab, then yes a good quality flooring grade sanded face underlayment can be used, and is the preferred choice over wood subfloor/framing systems.

I have that same bathroom. It's original to the house, which means late 60s/early 70s. I've tiled over one bathroom and am preparing to do the other one. The new tiles are so much nicer than the fiberglass pan. In our case, I don't think we could've tiled over the fiberglass pans: They weren't flat. Yeah, yeah, the new tile floor isn't completely flat either -- it slopes towards the drain -- but I don't see how it could work.

I understand the tile is not to your taste and at the moment you feel anything will look better. Your tile is dark and not my taste either, though it looks to be in excellent shape. However, peel and stick will not last in a wet environment and harbor mold and damp behind it, as it can not be 100% water proof. Paint is possible, but only if done professionally and even then it must be babied and will eventually begin to chip and peel away. Honestly, I would get a nice bright shower curtain that you enjoy looking at and hang it up on a tension rod covering the opening of the shower. Then I would lay down as large a washable or outdoor rug as you can fit to cover as much of the floor as you can. That will cover a lot of what you don't like. Then save as much money as you can to renovate the whole bathroom. I know that is not what you want to hear and maybe someone with more imagination can guide you to better short term fixes.