This looks really uncomfortable for Mio. I don't see it being that comfortable for Ritsu either, however with how she can bend her leg around Mio from under her and keep it up as she sleeps, this is probably very comfy for Ritsu. Add in the boob pillow and Zzzz♥
Ritsu is drawn far too small in scale for Mio, it makes Ritsu look like a little child.