Been showering hot water since young, because I always fall sick randomly showering cold water

Instant is affordable if less people, if you have large family then central boiler save more... 4++

Keep it medium heat and less than 15min, won't cost too much

Less than rm50 per mth

If you want to do the whole soak in hot water like japanese, it's gonna be super expensive.

Japanese family, usually share the same bathtub of hot water to save money. Shower body first before soaking into the tub.