You will need a RIGID CORE LVP to go over the marble. And that means THICK (10mm minimum = almost 1/2"). That means you will have a STEP UP where the vinyl meets the marble. I assume this will be in the doorways. So long as you are aware that the 1/2" STEP UP is a "toe stubber" in each door way and you are OK with that (every morning = toe stubbing event before you had your coffee), then go for it. And no....it won't look much better because then you will have multiple floors in MULTIPLE materials....which is almost as bad as multiple floors in marble. With the added benefit of the toe-stubbers in doorways. Sigh....I know. You do NOT want to remove the marble.....but it is the ONE THING standing in the way of you getting the floor that you WANT/NEED (which is PORCELAIN TILE). So long as the marble stays, so will your problems with finding a solution. Remove the marble and you remove the obstacles in your path. Leave the marble and you leave the obstacles. Your decision to leave it is the decision that is preventing you from finding a solution. You obviously HATE this floor. You have multiple threads going with the same issues in them....simply looking/hoping for some sort of solution. The solution = thick/rigid core Vinyl that is STABLE in sunlight/UV light that is laid over the ENTIRE FLOOR. And then hope for the best. This "rigid" core vinyl is some of the most expensive we have on the market. The most stable stuff for heat/UV is out of Korea and is hard to locate. It is $4+ per square foot. It will work. I recommend the ENTIRE floor be covered by the thick, high end, highly stable vinyl that is MADE for heat. No toe stubbers.

@parehm, We have Flooret Modin in Arbor in our entire house (actually just laying our living room and kitchen planks today!). We did extensive research and got samples of the Flooret, Provenza, Coretec Plus, Mannington Adura Max and Kardean. We chose the Flooret because it felt and looked the best, and we especially liked the extra wide and long planks, attached underlayment and 40mil wear layer. Some people don't like the bevel but we love it. The next best choice for us was the Coretec Plus, but it was $2 more per sq.ft and didn't look as good. We have a beach house and two 90-lb dogs that constantly bring gritty sand in on their paws. We've had the Modin in our master bedroom/bath and high traffic hallway for 9 months. This floor takes a beating and cleans up beautifully. The main negatives are the shipping cost plus having to deal with a freight company for delivery. But the company has been great to work with by phone with excellent response times and customer service. I always prefer to work with local dealers, but in the case, we have no regrets going with Flooret.

I've had sand & finish in place hardwood, engineered/glued down hardwood, and now LVP in a guest house. While I LOVE the real hardwood over 3/4" subfloor best for the softer feel on my feet and rich look, I'm satisfied with the look and wear with the engineered hardwood we replaced it with. (when we went from family room only wood floor to whole house wood floors, we had to put in engineered floors (or thought I had to), as we didn't have space underneath the appliances for the additional 3/4" subfloor). We recently installed LVP (SPC) flooring and it's my least favorite. While it looks great in photos, it has a plastic look and feel. I wouldn't do it again personally. It's possible that I just chose the wrong LVP. For what it's worth, our current engineered hardwood floors have been through two floods. In each case, we had fans and heavy machinery in the house for 3 weeks pulling out water. Contrary to water mitigation folks, who recommended we replace the entire house floors, we never did and 95% of the flooded boards still look good as new. The other 5% have the surface finish peeling, but lucky for us, it's mostly against the baseboards and isn't too unsightly. I need to get it repaired some day, but haven't bothered to so far and it's been 4 years.

Get unfinished engineered and have finished to match . Next best a prefinished engineered in a color as close as possible . Bedroom flooing can be different from the rest of the house as you have already experienced with carpet . I would not do carpet again if at all possible/