Their after sales service is legendary & they sometimes have shop soiled ones, might be worth giving them ring. Doubleboost on here does various videos demonstrating them on YouTube
Any 200a machine will just about stick your 6mm together.
If you want to future proof your purchase, go for a 250a set. You’ll need a blue 16a plug for those.
Most inverter based welders will work on a 13a plug as long as you don't turn them all the way up.
Ie, you could get a 250a welder now and run it at 180a fine then you still have the option to fit a bigger power supply in the future for welding bigger stuff.