What sort of floor is upstairs, carpet over floor, floor boards, etc... Underlay may work to a degree but it depends on how well you want the sound reduced. I can't see it being an acceptable solution as the thump will still resonate. Insulation between floors could work better when teamed with the underlay but would probably be invasive and you'd still have the thump's resonate.

yes to all, we did have the tiles professionally sealed, but sealing is not a cure all in my experience but I'm sure it helps considerable . my wife does buy those hand made goats milk styles soaps etc and I don't imagine there is anything more testing for stone, and yes it does mark. The Grey ( bane of my existence )granite much more so than the beige travertine ) I must admit though, the kids bathroom was almost non existent as one has sensitive skin and uses pump pack. I would also imagine climate, airing/ sunlight, volume of use and the time you have to manage it would also be contributing factors. We are way short on time and they don't get the attention they deserve, so I would suggest asking around, others may manage it better and it not be an issue. If your only doing your bathroom you may consider the risk factor not worth it for the volume, but for me, the advantage of travertine in the rest of the house far out weighs any marking issue in the showers, and wont stop me from using it again. To be honest when we sold the last house I just took to the shower with one of those paint scrapers with the razor in the end and most of it came off and it didn't detract from the look of the house. Sorry i have probably only muddied the waters even more, good luck with it.

Hi nice size kitchen, horizontal lines in your kitchen will make already long kitchen look a bit longer. looking at the pics of your kitchen it looks like u have a lot of horizontal line i would install the tiles lines vertically to bring the balance back. Number of lines will depend on the zones and the kitchen enterance along with dining furniture or vertical wall lights in the room. u may need to take a pic from the enterance of kitchen and draw a few details on the pics then work out the lines. Vertical lines are easy to over do so be careful. good luck

there is also a difference between ceramic and porcelain tiles - often these issues come down to a combination of (a) tile batch size/consistency (b) tiler's skill/capacity (c) communication in that if the tiler opens the tile box and he can't practically achieve what he thought he might because of the general discrepancies in size then they should at least speak to you before they start. So often with many issues in this game, it's about managing people's expectations and having open/honest discussions at the right time. When this breaks down, problems and disappointment is more likely to occur......so coming back to it, if you have high quality porcelain tiles that are millimetre perfect, square and flat then the capacity to lay them with minimal spacing is higher. Also the substrate/prep plays a part as if it's all out of whack and not perfectly straight/plumb/square then you'll be in all sorts trying to achieve the minimal tolerance detail.