I always start seeds indoors in March. Usually, by April, temperatures in southern Missouri are upper 30's low 40's. As soon as I can, I get them into a portable greenhouse with a portable heater. I don't think there is any substitute for natural sunlight.
This is what I use:
https://amazon.com/gp/product/B01GDV...?ie=UTF8&psc=1
You get healthy plants (though sometimes they are huge by the time I am able to transplant them.)
Just my experience for what it's worth.