I've been thinking about options to cover all basis and came up with this. To allow guests to use a bath/shower the ensuite would be shared. I added a wall in the master bedroom to divide it and add privacy so guests don't have to walk into the bedroom to get to the bath/shower. The upsides are that the ensuite is larger, includes a bath and shower and has more vanity room. Also, by diving the bedroom I can add sort of a walk-in wardrobe. The downsides are that there's only one bath/shower that has to be shared and guests have to walk through the walk-in wardrobe to get to it. Also, it reduces the size of the master bedroom but it's quite a long room anyway and it would cut out the light from the windows in the bedroom. Personally I don't see these as big problems but I guess some people won't like it. Do you think this is a good idea?

Thanks for all the great ideas guys! Just had the builder to view the flat and here are some updates: builder said the soil pipe seems to be straight down, but could install a pump to flush it; although the estate agent said the pipe goes from external wall at the back of the flat. Not exactly sure who is correct. the budget is likely to go between 30k-35k. I also had a measure of the current bathroom dimension which is 1.67*2.13m. and the ceiling height is 2.56m. we'll probably change the bedroom wardrobe and free up some space as well...

Where can I buy a walk in spa bath tub? Any suggestions would be much appreciated.

Both Hansgrohe and (Friedrich) Grohe are German companies; Friedrich was a son of Hans who went on his own in the 1930s, so they share a certain heritage. These days, Grohe is larger and no longer family owned. Both produce outside Germany as well as on their original German sites still. Both produce "basic" and "high-end" ranges. They're both regarded well back home in Germany, much of the choice is down to personal preference. Hansgrohe is on average slightly more expensive (but not on everything). They also own the Axor design brand which has a more "ecletic" selection. One can mix-and-match; in our bath (bit messy, sorry - we're using it for the washing up while waiting for the kitchen to be installed), the mixer is Grohe as is the shower wall outlet, the shower rail and head shower arm (just above the shower screen) are Hansgrohe pieces. At least the chromed finishes are very close for the two: Both can be sourced well below retail list prices - if you're prepared to wait, German online sellers for bathroom goods tend to have many-months delivery timelines. For Grohe essentials (the classical Grotherm mixers) at least, any German DIY shop stocks these at very attractive prices (the difference to the UK retail price list will pay for the ferry ticket and fuel).