Lettuce likes cooler temps from 40 F to 70 F . Mine have survived down to 32 F. These plants don't like it hot and will bolt. One year we went from 70 F to 90 F in a days. My lettuce bolted within two days of this happening. One thing you can do is move them into shade, that will help stave off the inevitable bolting. For a short period of time.
I don't plant my lettuce in the garden anymore. I use pots or colanders. With colanders, you have perfect drainage and I've never had a slug problem (yes, I know they have a God-given purpose but for the life of me, I can't figure out what it is!) The other nice thing is that you can have it more readily available to the house.
Short explanation of lettuce types:
Butterhead: Generally grown to full-size heads, butterhead lettuce has a beautiful ruffled appearance, with a blanched heart and a delicate, sweet, and buttery flavor. "
Lollo: Lollo forms loose heads with very frilly leaves that are often used for garnish. Lollo can also be used for baby leaf production. The leaves are characteristically wide, and can be used for wraps in addition to garnishes.
Oakleaf: These varieties form attractive, relatively dense, rosette-like heads of curly, crisp leaves that are characteristically deeply lobed and similar in shape to those of oak trees.
Deer Tongue: Also known as Matchless lettuce, Deer's Tongue lettuce is a loose-leaf variety that is favored for its sweet, nutty flavor and tender texture,
Romaine (Cos): Romaine is best known for its compact hearts of long, broad leaves. The outer leaves can also be used as wraps. The flavor is sweet, and the texture is crisp. Some romaines have a more open plant habit than those that form the classic tall, blanched hearts.
Summer Crisp/Batavia: As the name implies, summer crisp is the ideal choice for summer lettuce. It is relatively tolerant of hot weather and can be grown for either baby leaf or full-size heads. The full heads are heavy and compact. Summer crisp is also sometimes called French crisp or Batavia.
Loose Leaf: Loose leaf lettuce varieties are those lettuces that do not form a compact head. Their flavor tends to be mild and sweet. they can be used in salads, garnishes and wraps with their wide leaves.