I grow lettuce year round, although pickings are extremely thin this time of year. I also don't do hearts due to slugs, so it's loose leaf all the way for me. Most lettuce can be picked for leaf, just make sure you leave 6 to 8 of the youngest leaves each time you pick so they have enough leaf left for good regrowth.
Try searching for "rouge de grenoble” if you struggle to find those seeds, it's one of my favourites too and I also need new seeds, I've got 6 of them in the greenhouse at the moment and I'm intending to let one go to seed for next year. I tried to save seed last year outside but the wet weather killed the plants
My favourites are dark roden, red cimmaron, Paris Island. But I'm always trying new ones and seed mixes .