Good day
How did you get "permission from the mobile network operators"?
https://www.bakom.admin.ch/bakom...
Greetings and thank you
Patrick

Hello. I had exactly the same problem in the block and got myself a GSM repeater. You can find suitable repeaters from RosenFelt here: https://www.gsm-repeater-shop.eu/
Don't take the weakest repeater. A little bit of power is allowed.
I mounted the repeater on the screed. The signal is wonderful all the way down to the basement. So it also works with Sunrise/Yallo :-)

You must be thinking of a 4G repeater? As far as I know, this is generally permitted for indoor use.

OFCOM has a note on this on its website:
https://www.bakom.admin.ch/bakom...

For the 4G / LTE repeater itself, I would ask your mobile phone provider directly for a solution.