The most common and most likely answer to this crossword clue is the 8 letter word TWINSETS
I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "matching jumpers and cardigans /matching jumpers and cardigans" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case matching jumpers and cardigans /matching jumpers and cardigans = twinsets.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TWINSETS mean?
TWINSETS noun- A combination of a cardigan and a jumper, usually knitted in wool or cashmere.
- A pair of cars or locomotives that are permanently coupled and treated as a single unit.
- A pair of cylinders containing air for the diver to breathe.