I think you can very well still have plants in a windowless room- as long as you're willing to give them regular little 'windowsill holidays' in another room. I'd go with succulents, there are some great warm colour combos (see Pinterest for ideas) and the geometric shapes mimic your tiles. Of course, there are some incredible fake ones around too, saw one last week I could not pick from the real thing. I'd be tempted to mix in some of both to balance aesthetics with practicality! Separately, I'd be careful of adding any soft furnishings (rugs, spare towels, etc) to a small powder room. We are all aware these days that a flushed loo spreads germs a meter around it- I wouldn't want to be collecting and trapping them! I think (subtle) fragrance and votives would warm this lovely space without impeding hygiene.

Looks fab Interior Design By Jo. Like you said, small changes can make a huge difference!

The updated bathroom is so much brighter. Like the cabinetry offset like that-interesting. Wonderful job.

I have a separate guest toilet without windows using a ceiling extractor fan - not a problem. I also have internal cavity sliding doors to bathrooms and toilets and love how they give extra space and options regarding placement of items. Another location alternative for you may be between the cinema room and the kitchen, depending on what you had planned for that extra space in the kitchen. Two metres is a wide hallway, if that is what it is? Ours is 1.3 which is considered wide (as we need to accommodate a wheelchair which has to turn into doorways). An advantage of a very wide hallway is it gives room for extra furniture placement such as bookshelves, linen or other cupboards if needed. I don't see a linen cupboard or pantry cupboard in your plans. Something else to think about is future proofing - try to cover future possibilities with regard to function, as making structural or fittings changes later can be more expensive, and may come at a time when you can least afford it (e.g. injured, disabled, children, aging or other such people visiting your home). Lives change, sometimes over time, sometimes in an instant, and suddenly the doors are not wide enough (especially the toilet door!), or the walls are not strong enough for a weight-bearing rail, and a host of other things. We put 900cm doors as a minimum and it makes life a lot easier, including moving furniture in and out. Universal Design principles are worth a look. Sadly these considerations are currently considered special or optional, although there are moves to change that, so that builders and architects will consider these things as standard.