Morning, I would avoid the large drum and belt sanders for the advice already given, noise, dust and knackered sheets if not fixed correctly.
If you are prepared to spend a lot of time on your knees I would use good quality sheet sander and a detail sander for the corners and against the skirting.
Do a test with different grade sanding sheets / rolls and then proceed.
Good quality dust mask and extraction if possible.
Lovely view from the window.
Do this before others encourage you to rip it all out, fit UFH, ASHP and external wall insulation!!
Enjoy the Forum.