If you wanted, you could get a sink top toilet. In a 5x5 space, you could have just the toilet and shower head in the room. Use positioning of your fixtures to help with splashing. Use a shower curtian if you feel you need to. There are waterproof toilet paper holders and such that people use in wet rooms that might apply in this situation.
I don't know who is going to be using the room, but if there isn't sitting use required for the loo you could do a urinal instead of a toilet.
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Has really helpful ideas
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