Is There a Subfloor That Can Be Added Under Tile to Make It More Comfortable?

If there's anything that's not very strong underneath tile, it'll crack and you'll have to replace it. If I were you, I'd change to wood except in the kitchen and baths.

Dawn

A tile floor must be rigid or the tile will crack so no, there is no subfloor that will help you. The best you can do is make it warm. I have mats where I stand a lot. They are easy to replace when they get worn.

Another option is something like cork. Not as durable but will give you the comfort you want. There are other options.

I have had five knee surgeries, using the mats helps me love my floors, if that is what you want maybe give it a try. At least in my experience it isn't the walking on it that hurts, it is the standing.

We when got tile, they had to put new sub floor in to even out the floor. The sub floor has to be very solid, flat, and rigid. There is nothing soft you could put under, and install the tile correctly. It would start bowing and cracking.

I agree with Jo, it's the standing that hurts me. We have thick rugs, and that helps so much. I have one in front of the stove and one in front of the sink, where I stand often. That has really helped. We only have tile in the kitchens and bathrooms, and wood everywhere else. We have lots of rugs all over.

jo is right about the mats. in fact lots of places have ones specifically designed for standing for long periods. those would be good for high traffic areas or like in front of your sink in the kitchen. also my mom has a ton of area rugs on her tile. pretty and practical! (warmer in winter, too).

nope. If by comfortable you means softer, then logically a softer subfloor would cause the grout to crack and chip away and the tiles to crack and break as well.

Wood flooring is what you need.

Tile is the worst on your feet. We wear shoes throughout our house. I personally like carpet. Denial about how clean it really is. ;). But my feet didn't hurt.

Choose a different flooring.
ie: vinyl planks.
Carpet
Vinyl tiles, of which the high end good grade/brands of it, look just like tile and are even used in commercial installations and hold up well.

And there are different types and gauges of subfloor materials.
Depending, on the type of flooring, chosen.
If your existing floor is even etc., you can also install by professionals, another type of flooring.
We did that in our kitchen. Used to have tile, and on top of it was installed vinyl planks. Looks just like wood. Of course, we got professional flooring installers. They made SURE, the subfloor was, even, or they evened it out.

I would NOT choose ceramic tile or stone. In your situation with feet aches etc.
And you cannot "float" it when it is installed.

Go to a flooring showroom/store, and talk to the Professionals there.
To choose the right flooring.
There is even Cork, flooring.