Writer’s chair is too high (10)
I believe the answer is:
immoderate
'high' is the definition.
(thesaurus)
'writer's chair is too' is the wordplay.
'writer's' becomes 'I'm' ('I am' referring to the writer of the clue).
'chair' becomes 'moderate' (synonyms).
'is too' says to put letters next to each other.
'im'+'moderate'='IMMODERATE'
(Other definitions for immoderate that I've seen before include "Extravagant" , "Excessive" , "Reckless" , "over the top" .)