Thanks for the reply. When I was a guy at some point I did a bit of modeling and had the same issues, we had an in-house nutritionist, and he recommended to take 90gr of lean mean (could be beef sirloin, turkey, chicken) with every single meal, and some types of dairy products (among which a lot of cheese and yoghurt) every day. Avocado, salmon, nuts, grains...
As a girl now I am eating all that constantly and eating a lot! But it's not enough and I need to put more weight. I would just like to put on about 10 pounds of healthy weight. A lot of people in my family struggle with "not enough weight" issues.