One place needing no improvement (5)

I believe the answer is:

ideal

I'm a little stuck... Click here to teach me more about this clue!

'needing no improvement' is the definition.
(I've seen this in another clue)

'one place' is the wordplay.
'one' becomes 'i' (Roman numeral).
'place' becomes 'deal' (I can't justify this - if you can you should believe this answer much more).
'i'+'deal'='IDEAL'

Can you help me to learn more?

(Other definitions for ideal that I've seen before include "Utopian; yardstick" , "unlikely to be bettered?" , "example" , "just the job" , "Paradigm" .)

I've seen this clue in the Evening Standard.

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