Your son needs to increase his confidence in his ability to eat solids successfully. The more oral stimulation he gets, the better it will be. Allow him to mouth foods as much as he wants, as well as appropriate toys. Try a little teeth brushing as oral stimulation. Don't expect less fussiness about food as you enter the toddler years.
Toddlers are notoriously picky eaters.
They are also small eaters since their growth rate is down from infancy. Since he is your third child, you are well experienced in this area. However, your concern about Thomas's growth is understandable. The foods you say he eats are a nice variety. However, I do see a lack of vitamin C in the selection, and very little iron.