Lifting is great but you can definitely put on weight with the proper diet and calisthenics. Pound protein and clean carbs. 3-4 days a week hit a variation of push ups, sit ups, squats, planks, leg lifts, pull ups, chin ups, etc. If you do these properly and consistently you will put on weight. Just worry about doing as many or more reps than you did the day before. I lost 100 lbs and was really skinny, then I reshaped my diet and kept working out the same way and put on like 15 lbs of muscle. And I don't lift. So just let me know if you got any questions