Which nest box for which bird?

Hi, I'm interested in putting up a nest box on the back of my terraced house. The site:
-has no eaves / overhang
-north facing
-open
-not near trees or bushes
-fairly close to a big park with deciduous woodland
-not near very a waterway/lake
I have a tiny pond / glorified bird bath
Further around the back of the house, is a regular sparrow nesting spot, annually used. My understanding that martins, sparrow and swifts need overhangs. Robins nest low down. So, if I put up a small nest box like this, I would imagine I would get blue tits. Their populations are doing ok.
I am hoping to support struggling birds. Ideally this would be martins/swallows/swifts, but, as mentioned, I don't think this is possible.
I would welcome any creative thoughts on this.
Thanks
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I reckon if you are helping any birds to nest it's a good thing.