Hanes off Amazon

Uniqlo - might be a bit thin
Marks and Spencer - they may only have the summer weight ones in now
Go to Primark and see what they have
American brand Fruit of the Loom usually pretty decent for a good price

http://www.howies.co.uk/bundles-1/men-s-organic-cotton-blank-t-shirt-bundle.html

(i don't work for them!)

gap.

I'd check the fit of Howies before buying too many, last few years their necks have grown and their bodies have lengthened and thinned out.

Fruit of the Loom from various sellers on Amazon. Have a look round, some have weight of cotton in gsm. Pick some with the highest weight.

Cheap, so it's on the intensive chemical cotton farming, stitched by slave kids end of the market.

Gildan Softstyle are my current faves. About £4 from amazon posted, not thick though, very soft and thin but very comfy.

However as you want heavyweight, Gildan Premium heavyweight or heavy cotton are very thick for a T, I have tons of "ultra cotton" which are tad thinner and comfy all year round.

I've switched form Fruit of the Loom to Gildan as they are better quality and stitch. Generally better quality stuff has no stitch on the side from the armpits down, and flat covered seams around the neck (it's the last bit that persuaded me to Gildan from FOTL!)

I work in IT and I wear a lot of plain t shirts to work btw.

Ok thanks folks will have a look at those

Lands' end - mail order: their super - T's have been good.