I'll assume you have ceiling height so the space is not cramped.

Tile is often installed on a "membrane" to ensure that future cracks don't occur because of the slab moving 1/16" or so. There are ways to build a layer or two of the right materials to give you both an antifracture membrane, a heat break, and a small cushion. Many of these methods have not gone through the TCNA approval processes, so cautious professionals will be careful not to advise on this when their public reputation is at stake. A layer of cork is one material/method that has been used for centuries, but cork as an industry has not gone to the TCNA for approvals. I hope this helps you get the picture.

You can also heat the tiles, and this is in my opinion best done when some material separates the heating cables from contact with the slab. Otherwise, you are paying to heat the massive slab (and ground too) under the house.

Tile laid in direct contact with a slab-on-grade is always cool or cold, and always hard underfoot.

Can you try Marmoleum? They make some fabulous choices, even some wood look ones. It won't be as cold or hard and the design possibilities are endless.