Not a left handed mouse, but I’ve got an Anker Wireless Vertical Mouse – it was about £12 from Amazon.
I actually write left handed, but use a mouse with my right hand.
They don’t seem to do a left handed version, which is a shame as it’s really comfortable (looks a bit weird). Batteries last about 6 weeks (2AAA) and it ‘just works’…..
Not sure it would be a great shout if you need to store it in a laptop bag (it’s quite bulky) but I was getting really bad forearm/wrist pain from using the mouse at work (doing 3-D CAD monkey stuff all day) and this mouse sorted me out a treat…