Bolero fit

[7rider]

I have two arm coolers boleros. The M fits snug, but a little too short to cover all my skin in the rear. The L is too large in the arms, but covers more skin. (It's a bolero to prevent sunburn etc).

I think the M looks better, but the L provides more cover. Would tight sleeves make it retain heat better or worse? Are you going to wear it over a winter jersey, so you'll need more room? Do you want sun protection, or warmth?

I'm looking for warmth for cool morning commutes, where it warms up to short sleeve - or sleeveless weather for the ride home in the evening. Basically, for when it's too cool for short sleeves, and too warm for a jacket.