A few years back I used to weigh 10st6-11st and I'm 6"6'. I did 20-40 pushups a day in conjunction with already doing football training twice a week for a pub team which was mainly cardio. Was doing a bit of planch progression training.

I put on a couple stone in a few weeks and I've got a perfectly reasonable body right now. I'm by no means suggesting it as a means of getting stacked into some muscly super monster though. I'm reasonably bigger than the average guy and proportionately built with a triangular body shape at 14st. I used to be a skinny Jimmy and that was seriously accentuated by my height.

For someone wanting to break out of their super skinny problem I suggest keeping it as simple as possible, like I did. As soon as things get complicated people start flagging and fall off the wagon into average habits. Get past the major problem then advance onto more complicated stuff later.