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Not too snug at all. I've got the ladies L size and I'm 5'8, the top is definitely long enough to cover lower back when on the bike.
I keep finding good merino wool jumpers in charity shops in North London (Islington, Highgate, Crouch End, Muswell Hill) for a few quid each. Sometimes there's even cashmere jumpers! They may not be the most fashionable ones but they're great for cycling or hiking.
I got some Isobaa merino tops from SportPursuit (the 180 I think) and have been happy with them. https://www.sportpursuit.com/sales/isobaa