Re: how to get volume in hair after permanenet straightening....
There is no way if you're leaving it to dry naturally (which usually you do since otherwise you kinda defeat the purpose of having it straightened permanantely) but what I do in the early days post straightening is tip my head upside down and blast the roots dry for a couple of minutes and leave the rest to dry naturally which gives enough volume.
From experience - have had mine straightened several times over the years - after 3 or 4 weeks it looks perfect since the roots have grown enough to create some volume so it shouldn't be something you have to worry about for very long.
Btw, not washing your hair for 7 days? Have never had to leave it that long, I've always been told 48 hours and even that's far too long for me. But then again, I always have Yuko so perhaps it differs between treatments?