A lot of good advice from the Braves...how lucky we are to have such a board....left hand was a struggle for me too....I was told to keep playing it..no matter what...and it will come along with time....just like wine..it gets better with time/age...one thing I did, was played in front of mirror....as you know the motion of the bass side for waltz and 2 step...when I see my hand playing it, it sorta help me...if it did not look right I corrected it...but listening has more to do with that, you know when it does not sound right...anyhow good luck to ya and stick with it...it will get better with practice..practice...practice...

When I was a kid I learned to play piano-accordion.
It started with simple children songs and it's easier to manage the bass-side if you keep the melody simple. After some time it becomes an automatic thing with your left hand.
I don't need a metronome, because I'm one myself who drink to much