You'd want S3 sleep, which is where only RAM is powered and refreshing slowly. That was a good thing but S3 has been replaced by S0ix on many laptops. It's theoretically better than S3, as S0ix allows very quick state switching and low power active states where the system is drawing less power while you're doing low-intensity work like reading what's on the screen.

A proper implementation of S0ix requires the OS to do a lot more power management work though, so that's a whole lot for Linux to get right on various hardware configurations.

The manufacturers removed S3 aka deep sleep support after Windows modern standby appeared. You can now only have S2 on many Laptops and that's not lasting remotely as long.