I'd definitely start with a more neutral shower curtain. Having a clear or translucent one like you already have is a good idea to let in natural light. The shower curtain in my bathroom is clear with a white square pattern.
I'd look into some nice baskets for storage, or one of those cupboards that fits above the toilet. They don't have to be expensive, you can get them from Walmart.
I'd also get a toilet paper roll holder like this and I'd put it between the toilet and the sink. Mine is from the Dollar Store.
Poster in a frame, wall decal, or one of these. They have much cheaper shelves if you shop around on Amazon, Target, or a TJ Maxx type store. You could also make something with palets, just make sure you don't get the wrong type of wood, because you want one that's free from chemicals.
Got this one for my fiancé. It’s held up really well for a few years now. He’s rough on chairs but this has been worth the cost.
CLATINA Ergonomic Big and Tall Executive Office Chair with Upholstered Swivel 400lbs High Capacity Adjustable Height Thick Padding Headrest and Armrest for Home Office Beige https://www.amazon.com/dp/B07LFWR6LP/ref=cm_sw_r_cp_api_glc_fabc_fZK6FbNWMAASY?_encoding=UTF8&psc=1
Recently got these bamboo sheets because they were highly recommended here on reddit(forget where exactly, I just searched for sheets).
For $45, they feel much more luxurious than they should. So. Soft.
I think that might be a GU24. [https://www.amazon.com/Sunpark-13-Watt-60-Watt-Incandescent-Equivalent/dp/B002BFO3KK](Look here). I think GU13W is just the model number. That socket looks like a standard socket. This is what a GU24 socket looks like.
Idk if this is on the Amazon UK site, but if you have a bathcaddy(great for reading!) you could Velcro-tape one of these warm closet lights to it. Not waterproof, but not necessary on a bathcaddy.
ZEEFO 6 Pack Motion Sensor Light, Battery Powered Motion-Sensing LED Night Light, Wall Light for Hallway, Closet, Kitchen, Step, Stairs, Bedroom, Bathroom, Nursery (Warm White) https://www.amazon.com/dp/B01MDKI6U4/ref=cm_sw_r_cp_api_I2qPybTTSZ7PB
I have a wooden shelving unit from Ikea that stands over the toilet; I have some big natural fiber baskets to hide all my junk in and it lets me keep my towels within easy reach.
I'm not sure the aesthetic you're going for but I found this one on amazon that even has a cabinet! https://www.amazon.com/dp/B00B5H9CJW/ref=cm_sw_r_cp_api_aJ2FybMBFM3DS