Admittedly not bike specific, but I just purchased a couple of John Smedley, Olympus knitwear pullovers in TK Maxx.

Crew neck Extra Fine, New Zealand Merino, Made in England.

Too figure hugging for my ‘sensuous curves’ for civvy use, but will be great as long sleeve a base layer for winter commuting, if a just a smidge too short at the back when on the bike.
Really fine knit … I was wearing my howies base layer at the time so I had a good comparison.

£24.99 each (they claimed original SRP was £100 ouch)

Cool stripey/bright colours.

If you want to bodge even more, there were some ‘Refectory‘ branded, slightly heavier weight merino items there too. a little looser, but could probably go a size down to figure hug. Coarser weave, but only £16.99