Having looked at the Mary Portas armery, the M&S arm control, and wearing long sleeved t shirts under stuff for ages, I bought a Wingz sleeve thing last week, and it is brilliant - in the full length tall, it comes right down past my wrist, and fits well. No bulk, covers armpits, and as its bra strap level, doesn't interfere if you have a shaped back of dress/top.
Makes a difference for me as I have a lot of scars on one arm that also has to be kept warmer, and I don't really like cardis.