I don't have experience with travertine. We put porcelain tile flooring in our kitchen about 8 months ago and I love it!! It's extremely durable and easy to maintain. I just go over it fairly quickly with a rag that's been dipped in warm water and wrung out. A friend of mine has porcelain tile, and loves it, as well. She has an elderly Bishon dog who is prone to accidents. She cleans it up and the floor is like new. I'm not sure if she uses just plain water..I didn't get into that detail with her. We bought our tile from Lowe's. Dh had experience laying tile for us in the past, so this was a DIY project. Our total kitchen size, wall to wall (without cabs is about 11' x 11', so our floor area is small. We used 18" x 18" unrectified porcelain. The tile cost was $2.45/sq.ft. It's not labeled as being "through body", but the color on the bottom & sides of the tile is the same as the creamy base color on the top.

Travertine, as stated above, is touchy about the freeze-thaw cycle and also does not like moisture build-up underneath it. And, as @Red Berm states, "think red wine, and weathers in acid rain." While beautiful, the conditions would have to be perfect for me to consider Travertine for a patio here in Chicago. That being said, if you are in a more temperate climate, Travertine has wonderful character that is hard to duplicate with a concrete paver. I would not worry about the gray on gray issue. Being monochromatic can be a blessing as well as a curse. You can make the space jump with container plantings, contrasting furniture or other site amenities. If you look at the monochromatic pool deck below there is an enormous difference from one photo to the other. Orange cushions are original to the design, but two years later were replaced by off-white cushions for an even more subdued space. Good luck with your project and post a few photos when you are finished!

OK...so you have a LIGHT floor (weight wise) currently in place. That means the original build PROBABLY had been built to handle a light weight and FLEXIBLE material like sheet product (linoleum or vinyl.) That means you have a 99.9% chance you will need to add more thickness to your subfloor. Ok...now we get into the nitty gritty. Regardless of stone or tile, you will need this beefing up (unless of course to TOTALLY luck and find you have a house that was OVER built and has WAY TOO MUCH subfloor material for the surface it holds = doubtful). Good. Now look at the transition HEIGHT between the existing sheet product (probably vinyl but could be linoleum). Is it even/level? Is it CLOSE to being even/level? Is it so close you don't notice the slight (4mm or so) height difference? If I'm right, there will be very little height difference between the floors OUTSIDE the kitchen and the floors INSIDE the kitchen. That's where the problem is going to be...the floor-height transition. Imagine you have to ADD 1/2" plywood just to get a subfloor that is stiff enough to handle tile (or possibly 3/4" to handle stone). Now imaging a tile/stone floor that is another 3/4" HIGHER than that. The worst case scenario is you have 3/4" plywood + 3/4" stone = 1.5" TALLER than the current kitchen floor. Now we have issues. Big, nasty, technical issues. Your entire kitchen design is going to centre around the floor height issues. Are you doing a complete gut of the kitchen? Do you have current photos of your floor heights? Do you have wood joist subfloor system in the kitchen? And with a floor/home this old, have you don't testing for lead/asbestos?

Sorry, I realized my comment never even posted! So weird. Thank you so much for the recommendations and for your long response, Beth!! Those are GORGEOUS and I can’t believe the difference the trim made on those peninsulas. Thankfully my dad is a carpenter and can do just about anything so I’m sure once I show him the photos he will have it done easily!! :) just needed some ideas and inspiration. I love all of the options.... but I might like the idea of leaving it just plain (with no shiplap or board and batten I mean) but I also love the idea of the tongue groove. They’re all so beautiful. I have no idea what a “toe kick” is though! That’s new to me :)