Kate KasinWomen's Basic Long Sleeves Mesh Sheer Tops

Can this be worn as a base layer, under a sweater? I am looking for a barrier between itchy sweaters and the skin, not thermal wear.

If I usually wear large should I order extra large

I've ordered these in several colors but grey and the dark grey are my favorites. seller - please get size small in stock in grey colors

Is this more White than ivory?