-
Thank you for your suggestions.
Ironically Uniqlo and Muji have their stores right next to each other here in Berlin and I been to both recently.
While being in the former was just an overall annoying experience Muji was very nice.
Both do tend to have like the opposite of "slim fit" cuts though usually, it's made for rather short people, to be frank - also there's not much in white or light grey, so no use for me.
Uniqlo are pretty good, although might be a bit thin for your purposes;
https://www.uniqlo.com/uk/en/product/men-extra-fine-merino-crew-neck-sweater-400623.html?dwvar_400623_size=SMA001&dwvar_400623_color=COL67&cgid=IDextra-fine-merino2246
https://www.uniqlo.com/uk/en/product/men-premium-lambswool-turtle-neck-long-sleeve-sweater-412365.html?dwvar_412365_size=SMA003&dwvar_412365_color=COL01&cgid=IDlambswool2248
Muji also often good;
http://www.muji.eu/pages/online.asp?Sec=1&Sub=22&PID=10239&qclr=4550002726171
http://www.muji.eu/pages/online.asp?Sec=1&Sub=22&PID=10061&qclr=4550002727499