Paul, the acoustic foam will do very little to nothing for heat retention. What is on the other side of the block walls?

Gaps between solid surfaces are what help for heat retention. This is where putting up sheetrock, gypsum board, etc. (not sure what it's called in UK) with a gap between it and the block would be helpful for thermal insulation purposes.

Don't bother with the sound board if it's just the sawdust based type like they sell here in the US because it's designed to go in between relatively acoustic transparent surfaces. Here in the US it's often used between adjacent living spaces for 'stick construction'. You don't have that issue with the block walls.

That is a pretty narrow space. Monitoring using your monitors will be problematic because of the room modes that will be present at fairly significant levels due to the small size.

Type in your dimensions here to see what I'm talking about:
http://amroc.andymel.eu/?l=200&w=390&h=350&r60=0.6 I took a guess at your height, and used 390cm (didn't include the high shelf, but you can run one of these simulations adding in the additional length. That website also gives direction on absorption amounts needed to tame modes. Modal density is pretty thick with those dimensions.

I would suggest investment in some very nice monitoring headphones now and begin getting used to mixing on them in your current space.

I don't see any microphones in your current room, are you doing any mic recording? These modes will also affect recordings.

-Scott

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