Learn from my mistakes!
Have you got room for the extra long, extra wide P shaped baths? They are only something like 10cm longer and 10 cm wider.
My parents had one of those put in and it is amazing for both showering and bathing. Children can practically swim in it... I didn't have room and to be fair the short and normal width P bath is plenty big enough for showering.
Don't just get a fixed rainfall head - I hate that when people just have a fixed rainfall. You need an adjustable hose head too.
The space I want to put the bath is longer than the length of the bath, so not sure whether to put a heated towel rail on the opposite wall to the shower, or maybe shelves on that wall for storage of bottles and towels?
Unless you get one of the fancy folding screens that enclose the top bit of the bath, anything here will be in the spray zone and get wet.
I wish I had got a J shaped bath with screen like this
I would also get UFH as well as towel rad. I didn't do this and I regret it every day in winter.
I would also have got a duel source towel rad (elec and heating) because mine is only on with heating and that is not enough.
100% get back to wall, or wall hung toilets and vanity units. I got a nice vanity unit with draws underneath, surprising amount of space in them.
I got a lovely mirror with lights and demister pads and shaver socket - absolute winner. It was this one and I love it every day. So easy to do my eyebrows, so easy for DH to shave, toothbrush always can be plugged in.
decent shower basket for bottles noooooo I have a 'no bottles out' rule. Everyone has tubs on the shelves for their stuff. The bath and shower area has to be kept clear.