I buy from Cookson’s every month and here is a list of the products
I like to keep in stock:
Round wire; 0.8mm, 1.0mm, 1.2mm, 2mm, 3mm
Square wire; 2mm, 3mm
Sheet; 0.5mm, 1mm
I make everything from that combination. I also roll my own sheet
from melting solderless scrap - this gives me sheet of differing
thicknesses and in big enough pieces for projects that my stock
doesn’t cover. The square wire, I either use as is (which looks
beautiful twisted) or roll to a more rectangular profile for making
ring shanks or parts for pendants.
BTW, I just tried 950 palladium which you were asking about the
other day! It’s great and solders as easily as silver - as long as
you have a hot enough torch - and it requires no flux!