I agree with OR, and that's based largely on my own experiences as a [kinda ex-]ectomorph, having got a lot stronger already over the last year and a bit. What's helped me more than anything else is the big lifts, and eating big. WIthout a doubt.
So, keep it simple. Even better, pick a good routine, like the MAB full body rep goal one, say. Keep progressing with it, every session. Eat more food than you think you need to. Make all kinds of gains.