DS is 3 and in 3-4 sizing atm, but is about to spurt into 4-5 
I'm looking for cheap, long sleeve plain tshirts for him to wear as a vest under his (bought last year in the sales for this summer!) short sleeve t-shirts (Skinflint? Moi?!
)
I've looked in ASDA/tesco/sainsburys but they all seem to be either thermal, or plain vests/shirt sleeves.
Any ideas? Ideally I'm thinking about black, grey, navy to contrast.