Holiday home floor / screed insulation: to insulate or not?

Dear people in the forum,
I have a question for you regarding my holiday home: I took over the house (on a slope) this spring and have now removed the entire interior construction and structure from the GDR times and early 90s...
Now the shell structure (exterior walls to be plastered, installation and gravel subfloor) stands on the slope.
Until now, there was a screed in the house - cracked in some places - which was laid on a sand subfloor.
Now my question: Is it appropriate for use as a holiday home (including winter use) to build up the new floor with foil, sub-concrete, bitumen layer, insulation, and screed? Or, in your experience, is a simple build-up with foil and screed sufficient?
I would then like to grind and seal the screed - possibly have a wooden floor in one room.
According to my logic, a complete build-up with sub-concrete, insulation, etc., after not heating for a week in winter, would be just as cold on the feet as the complete build-up with insulation - because at some point even the most gigantic insulation simply cools down - is this assumption correct or nonsense? What do you advise me if I want to spare guests in the house from frostbite on their feet and also feel comfortable myself in winter?
I thank you in advance for all hints, opinions, and tips (please also feel free to name sensible alternative constructions).
Best regards, Michael.

Insulation is not about cooling down, as insulation cannot store heat. It is rather about preventing cold from coming through from below. That already says it all: insulation is recommended here as well. For something like this, I like to use 8-10 cm Linizherm or equivalent (adhere well).

Thank you for your response, that makes perfect sense ... so insulation would be the way to go - now the question arises for me - is it technically sensible to choose a simplified version of the floor structure - meaning - the base of the hut (sand filling), insulation, foil, screed - or MUST there be a sub-concrete with bitumen for this system to work at all or make sense? I would like to avoid it if possible - to move 4-5 m3 of soil down the slope ... without this action, a structure with sub-concrete would not be possible because the level inside the hut would be too high ... Best regards Michael Nager