advice on what to wear under cardigan

[AuldAlliance]

Have this in white this cardi (click on "autres vues" to see on model). What can I wear under it other than plain white long-sleeved T-shirt? Collars look a bit odd... Any hints? TIA

Well the model seems to be wearing a scoop or boat necked t-shirt, possibly a vest - how about those? As it's white, almost any colour, I'd guess. Pretty camisole?

I like these thermal trimmed tops .
Or a black polo neck?