Having a best-selling record myself (6,3)
I believe the answer is:
number one
'myself' is the definition.
(I've seen this before)
'having a best-selling record' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'one' and 'one' is present in the answer.
The remaining letters 'number' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for number one that I've seen before include "Top-of-the-charts hit" , "top-selling record" , "top man?" , "Yours truly" , "leader" .)