If you shop for a space saving toilet there should be plenty of room for a full sized basin on the same wall. A p shaped bath would also give you a little more room at the shower end.

Thanks pjbell! My first thought was 'no way, we use bedroom 2 and can't lose it - far too radical'. But then I stopped and looked and actually, that may well be worth considering! All bedrooms are in use - bedroom 2 is our studio/craft room/office. Kids are in the back bedroom and top floor. I've got my heart set on an en-suite and keeping our large bedroom but have been mindful of making the studio too small so was opting for a small shower room. I've been pondering if there is anything we could do to have a larger family bathroom but couldn't see how. This could give a large family bathroom and more luxurious en-suite. The back room is south facing so would be much better for a studio - its worth seeing the size if we split into two bedrooms. I do like the fact that all bedrooms are decent doubles and wouldn't want them much smaller. We are going to be here for the next 10-15 years and will then look to downsize when the kids have flown the nest. This will be the only major work we'll do so although it needs to be right for us, I also want it to be as appealing as possible to the next family. Definitely food for thought - thanks!

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

If you intend staying here for a decade then you should make this house work for you and not the next people. I think that since you have already flagged extending in 10 years you should also future proof your plans now. If it were me I would have a bedroom where the current big bathroom is in order to give you the possibility of later extending over the ground floor extension. I would also want a super sized bathroom for my use - I have always believe the person paying the mortgage should have a better bathroom than people who visit three times a year. And I would take the view that when a loft bedroom is later added it won’t matter if one of the four bedrooms is compact. So I offer an alternative.