If anyone is having a hard time with transplants, I would highly recommend soil blocking. Much less transplant shock.
I start mine in an unheated hoop house. I built wooden trays and cover them at night. It keeps them a little warmer and prevents mice damage.
You’d be suprized that things like tomatoes and squash can handle the cold (20’s F) nights if covered and will still germinate during the day when it warms up. Some plants (basil) not so much.
Spring time is too irratic here for directs seeding most things. 20’s at night, 80’s in the afternoon sometimes. Very few plants can handle those swings when they’re young (fava beans seem to be the exception).
I have better luck direct seeding in the fall (mostly leafy greens)