ebang,

It is the air temperature that can affect blossom setting.

Some varieties to look for are Glacier, Mountain Princess and Nepal. Annapolis seeds might be a good resource for you.
Have a great learning adventure.

I hear that sometimes the heirloom ones don't do so well in our cool-nighted climate.

It is the air temperature that is tied to lack of fruit set (aka Blossom Drop) - see link below. But it makes no difference if they are hybrids or heirlooms. Both are subject to the same environmental effects so if you can grow hybrid varieties then there are plenty of heirlooms you can grow too.

Dave

Here is a link that might be useful: Blossom Drop FAQ

Stupice and Moskvich are two you might try. Also get a Territorial Seed catalog, which has information on heat units required for some varieties of tomatoes.

I grew Cherry Chocolate (Chocolate Cherry?) last year, and it tasted better in cool fall weather than in our hot summer.

Here is a link that might be useful: Tomato microclimates - cool summers

Not clear if the non-gardening boyfriend wants to grow these or if he wants you to grow them.

If he wants you to grow them, make sure he does the grunt work in the garden. I've tried maybe ten heirloom types, and never got more than five toms off any one plant.