Tupperware makes a collection of containers called Fridgesmart. they have little buttons that control the moisture content of the inside. I have one of the old round models that I use for lettuce and it will keep several weeks. It is just me and like you, I don't eat salad every day but love the leaf lettuce. I have also found that if I buy the lettuce any variety whole and not cut up in those bags, it lasts a lot longer.
here is a link to one like I have on ebay....
https://www.ebay.com/i/182842289935?chn=ps&dispItem=1