I’ve found that Grenoble Red lettuce (batavia var.) performed exceptionally well for me last year. It’s recommended by CD as well. Picking the outer leaves a few at a time from each plant kept me going through most of spring and summer. It bolted eventually, but I was amazed at the rate/speed of growth in high summer. CD has a very informative video of lettuce growing where he names a few varieties as well. Best of luck
May I also add, since it’s a ‘bog plant’, it likes a well watered soil at all times, that doesn’t drain too fast. So that’s a challenge if we again have a summer like we’ve had last year.
I am growing the very Franchi seeds Red Grenoble variety and mine are doing very well, using Charles Dowding’s method of pricking out seedlings into trays. Maybe it’s a fresh batch I bought in spring from Seeds of Italy.
Hope this helps, and best wishes.