In addition to the structures Mike proposes, many people include the invitational 4-card raises into 2NT as well as the GF hands. Now it's possible to sign off in 3M after 2NT LR+ with a 3♣ bid (any minimum hand). The structure I play with some people includes 1M 2NT 3♣ being minimums, 3♦ being mediumish hands, and other bids showing maxes or showing voids. Various relays after 3♣ and 3♦ allow both hands to reveal shortnesses. So we wrap a few extra meanings into 2NT and lose a little bit of cuebidding accuracy, but we get some gains in pinpointing voids/singletons and the relative strength of opener* *This is in the context of a strong club system, which is probably outside the scope of what you're interested in, but it just means the ranges for minimum, medium, and maximum are a little more narrowly defined. My structure is probably less suitable to a 2/1 system, making Mike's suggested followups probably better.