I like fire doors.
As well as blocking fires when they are shut on an unattended room, for example at night, and protecting your escape route by preventing fire and smoke in the passage and stairway, they are heavy and substantial, feel good, not flimsy, and are good at blocking noise.
Cheap hollow doors are made of air with a thin coating of hardboard or ply and are complete rubbish.
My favourite is this style (it helps if you have, or like, an Edwardian house). This one is made by Premdoor and is available from various sources. It is suitable for painting. I would avoid the ones with a fake grainy surface. Depending what you like and what you can afford, you can also get veneered or solid wood doors in a great variety of styles. You can get non-fire doors to match, for example for cupboards or non-habitable rooms, but I recommend a heavy, sound-blocking door on bathrooms and cloakrooms
You will need three suitable hinges, as the doors are very heavy, and I recommend lift-off hinges. You will most likely need new door lining ("doorframes") to suit. You need a slightly longer latch or lock than usual. An older house will look better with a 100mm or 150mm backset and knobs.
A joiner or carpenter can fit doors much better and faster than a handywoman or general builder, and will also know good local sources of doors. For best resistance to smoke, draughts and noise, and if building regulations require it, fit furry pile "brush" smoke strips to the grooves in the frame, and inject fire-resisting expanding foam between the wall and the lining.