I started gardening because I eat a lot of lettuce. I have experimented with many varieties. I also label my packages with "heat tolerant" or "cold tolerant". Direct sowing has not worked well for me. I couldn't figure out why for months until I noticed tiny little ants running off with my seeds.
Now I start them indoors, similar to micro-greens, a shallow tray with an inch of soil. I keep it pretty wet and transplant when the seedlings are about 3/4 inch high. I just wet the soil really well, like to mud pie consistency, then grab a handful of mud that has at least one seedling and place into my raised beds. Water immediately and thoroughly and the shallow roots find their own way into their new home. I do this throughout the summer. But sometimes it gets too hot in my house to germinate new seeds. I am experimenting with some different green for the hottest part of the season this year...purselane, burnet, and Malabar spinach.