A bidet. We got one with heated water and seats and going to the bathroom feels super luxurious now. Not to mention all the toilet paper we save and increased hygiene.
Problem here is getting electrical to your toilet location? I was thinking about that too, but I didn't feel like making the leap to hiring an electrician to install / create a new outlet there.
Its going to be a _little_ tricky to get lines to the other bathrooms, but I'll figure it out when the time comes.