Sounds about time for a new chain/cassette then, maybe chainring but I'd probably try without first to see what it feels like if it doesn't look obviously worn, shifting might be due to wear but more likely indexing or in need of a new cable and maybe outer.
The chain is relatively new. Only a few months old and I've not done a huge amount of miles since it was replaced. The cables are super cheap but the outers are kind of fancy. Will try replacing both and get someone more competent than me to index. If that doesn't work, new cassette time in spring!
Sounds about time for a new chain/cassette then, maybe chainring but I'd probably try without first to see what it feels like if it doesn't look obviously worn, shifting might be due to wear but more likely indexing or in need of a new cable and maybe outer.