Dog’s plaything originally designed in SW resort (3,6)
I believe the answer is:
toy poodle
'dog's' is the definition.
(toy poodle is a kind of dog)
'plaything originally designed in sw resort' is the wordplay.
'plaything' becomes 'toy' ('toy' can be a synonym of 'plaything').
'originally' suggests taking the first letters.
'in' is an insertion indicator.
'sw resort' becomes 'poole' (resort in the South West of England).
The initial letter of 'designed' is 'd'.
'd' placed within 'poole' is 'poodle'.
'toy'+'poodle'='TOY POODLE'
(Another definition for toy poodle that I've seen is " Miniature curly-haired dog".)