Black Bear, if your temperatures are not hitting the 90's, there are probably lots of early and pretty cold tolerant tomatoes that will do fine, maybe better than the 'strictly cold and early' ones.
Black Early, Pervaya Lyubov, Chernomor, Yaponskiy Krab, Amazon Chocolate are some of the slicers that set up well here in cool and then ripened up nicely once they got used to summer sun - as early or within a week of Stupice. And I'm sure there are more - I'm trying a few new ones at least every year.
With my greenhouse, I can go as far as "early midseason" types, but only the select ones that will happily grow and set fruit below 70 F. I mostly go for early ones with a few early-mids, in case of a really bad year.. Late types are not an option, I guess you understand.
As regards the early reds, I've tried a bunch and liked a few. Still many I haven't tried. Stupice and Moravsky Div are reliable. Kimberley is earlier and pretty good but maybe not quite as cold tolerant. Best tasters for me were Alaska and Napoli a Fiaschetto. Cold Set and Siletz were decent to eat, but they basically burst every fruit - it does get hot in my greenhouse when the sun shines! I really like the early orange ones Zolotoe Serdtse and Orange-1 (aka Belarus Orange) but they sunscalded really badly when we had a month of extreme sun last year.