I'll report on our old building renovation. Underfloor heating was also a top topic... We don't have high ceilings, so we didn't want to add height. We decided on a water-based underfloor heating system, which is fed by the return flow of the regular radiators. These heating coils are laid directly under the tiles, so there is no loss of height. It has worked perfectly for 12 years, and although it only provides heating, we don't use any other heat sources for these rooms (even though they are available). In addition to this water-based system, these thin-bed heating systems also exist in electric form. But if you really renovate, meaning tearing down walls, moving them, etc., you should consider raising the door lintel and removing the screed to install a proper underfloor heating system.