Sturdy onesie? Trouble is, sadly, I must be squeezed into it (6,4)
I believe the answer is:
boiler suit
'sturdy onesie?' is the definition.
(type of one-piece garment)
'trouble is sadly i must be squeezed into it' is the wordplay.
'sadly' indicates an anagram.
'must be squeezed into it' means one lot of letters goes inside another.
'trouble'+'is'='troubleis'
'troubleis' anagrammed gives 'boilersut'.
'boilersut' placed around 'i' is 'BOILER SUIT'.
(Other definitions for boiler suit that I've seen before include "Protective clothing" , "Workwear" , "Overall" .)