"...what about a poncho?..."
Another vote for a poncho, however if you to lift and carry things maybe not so much, I often wear my 58 poncho atop my Swanndri Bushshirt, that can work. I don't worry about leggings so much as I wear shorts for ten months of the year and waterproof the top of my boots with bits of cut up rubble bag tucked into my socks and pulled down over the boot top.
I have used Barbour jackets, usually bum length ones and those were used for 'country/farm' type activities, A long time ago I had one of their trench coats which was extremely comfy and kept me dry in windy and wet Edinburgh winters.
The Barbour stockman type coats may well be worth a look, you can often find cheap ones in various states on ebay, so you could try out an old ragged one before you fork out for one that is new.
You could also look at something like this which looks like it would do the trick (at a price).
Swedteam Anorak Titan Pro
Let s know how you get on.