Start your seeds indoors now. Use a post hole digger and dig an 8" diameter hole about 3-4ft deep in your garden now or this spring then mix in some fertilizer with the loose dirt as you put the dirt back in the hole. This way the roots can go down deep and the hole will hold water like a barrel for a few days. I did this hole digging last year and it saved my garden during the long drought.
Don't set out all your tomato plants out in the garden at the same time as some of them will die. Yes you will be able to set the plants out during the days and bring them in at night, this will help them adapt to the cool weather.