Re: Which covers fit over Sandy's?
Did you add the extra layer of fleece through the wet-zone in your fleece longies? That should take care of compression leaks as long as the diaper isn't super soaked (and if it is then maybe try adding a doubler).
As far as the "pj pants look" I think if you stick with solid colors, especially darker/neutral colors, they will look more like pants and less like cute jammies
I've read many posts about the coverage/easy-on/breathability of Bummis super whisper pants that are made of nylon and scrunch down under clothing...maybe try those?