Nice places to stay in Cardiff?

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Hoping for some recommendations. I am taking dd to Cardiff (Dr Who stuff) and we need to find somewhere to stay for a couple of nights.
The complications are she has ASD and anxiety so we need to be somewhere low (3rd floor or lower) and she's not happy about bed sharing so twin beds would be best.
We will have a car.
Don't mind if it's a hotel/air bnb/other variation. Preferably not eye wateringly expensive :)
not the premier inn at the M4 services either

Travel Lodge? We've just stayed in the Whitchurch one which is only 3 floors. I'm sure they'd do a twin room.

you can hire appartments over the bay. its walking distance to dr who stuff and the bay has loads to do. look on air b&b or google Cardiff bay apartment weekend lets

This is the Air bnb I have booked for the second week in Aug. It's 3 rooms and a living room in the owner's house with use of their kitchen.