@Fishel Tessler , I hope you are not discouraged by the various cautionary comments you have received. Your proposal is a creative option for boutique lodging. You won’t know if this wins over your guests or has them wishing you’d just given them a guest bar until you try it.
If there is enough space on the bathroom vanity, you can display options- a small log on a beautiful little tray with an attractive vegetable peeler. (I might have to peel for awhile before getting enough soap peels to wash this old bod …) You could also have a small bowl of attractive guest soaps in various interesting shapes and colors – ducks, dolphins, shells, roses , astronauts …. Whatever your theme might be, and then some straight up guest bars.
I don’t think it will be that hard to find (or come up with) a recipe that stays soft but firm for a long time. As
@Ephemerella says, she has one.
It occurs to me that I made such a batch about 6 weeks ago. My normal recipe seized so bad (due to combo of fragrance oil and too many additives) that I added at least one cup of boiling water into a 1000g batch of batter. I was then able to chop it up, and soften it enough to scoop and press it into a mold. It looks like meatloaf, but an actual recipe that wasn't an accident should be more attractive.
Out of curiosity, I went down to my basement just now, I tried shaving off some slices with a vegetable peeler. No problem!! I also tried cutting it with a small appetizer knife. No problem!!! So, I think what you want to do is completely doable. The question will be whether, in the end, it works out as you envisioned.
In case you are wondering, my recipe for my 1000 gram loaf that is still soft was: 40% Lard, 20 % Coconut oil, 6% Tallow, 4% Shea butter, 23% Olive oil, 7% Castor Oil. Then, too much espresso grinds, too much oatmeal, a fragrance oil that seizes so bad it turns into a rock, then at least a cup of boiling water. I have wondered if my soap might get moldy from so much excess water and being soft so long. No mold yet. and the best thing about this soap so far is it smells great!
I think you can probably find a recipe on the internet that is tried and true, and for the purpose you suggest. Good luck and keep us posted!!
But, I’m just saying that what you propose seems doable. No one is going to get cut on either the vegetable peeler or appetizer knife I used. It's true some guests may take more than they'll use while at your place, but that might be a compliment and good advertising. But, don't give up on your idea until until you"ve tried and find it doesn't work for you!