1500 & 1800 is a bog standard (generic) bath size. What's the size of the bathroom, 1450 x ? and where is door and window, existing layout.... Most of my clients still prefer a bath in their houses. Even with a shower screen over bath. A renovation of existing bathroom with bath/shr/toilet/vanity in same positions may be all you need.

Too dangerous with normal tub , the best way to do this is too build the bath in a normal rectangle shape and height with concrete, make the side of the bath facing the room approx 8- 10 inches or wider if space allows so that you can sit on it to get in and out of the bath, then cover with small plain mosaic tiles including the walls, You can have a shower screen or a good old fashioned curtain or nothing as long as you have the drains in place. They do baths like these in Asia and safely have the shower over the bath no slipping., they look and are special too. Safe for everyone to use, perhaps not the elderly who should only use separate showers with a stool etc. cheers,

Aluminium does under go oxidation, although it is white. Unlike iron oxidation which is orange. If the tile is designed for use in a wet area it is probably coated or anodised to prevent white oxidation. Check if cleaning will be a hassle (risk stripping the coating).

Look at what shampoo bottles you use and size accordingly. I know we have 2 pump bottles pls bath liquid and a couple of extra it,es for individual needs.