I'm concerned that I am not giving him enough protein and iron
Sounds to me that you feel you're depriving your son by not giving him meat (or maybe someone is telling you that you are!). I really don't think you need to worry. The fact that you're thinking about this probably means that you are already being very careful to balance his diet.
My LO is now 2.5 yo. We don't have meat in the house since I do most of the cooking and wouldn't have a clue where to start with it. He isn't crazy about drinking milk but eats lots of cheese and yoghurt, also tofu, eggs, beans, chickpeas and lentils (for protein). As far as iron goes, that comes in dairy products and also from dark green leafy veg. If you are concerned to maximise absorption of iron from these, you can combine the veg with something citrusy: butter and lemon on broccoli or a drink of OJ on the side. I had a period of concern that he wasn't getting enough of these and hit upon the idea of making a savoury spinachy lentilly purée and putting it in a tortilla wrap - he'll eat anything in a wrap!
You say your LO has gone off tofu, just keep offering if you want to keep it in his diet but try it a different way, maybe tofu burgers, sausages, soy yoghurt or ice-cream. Or maybe it's a texture thing, if it was soft tofu, offer firm or vice versa. Smoked tofu is a hit in this house and is very good with broccoli and pasta (tonight's dinner!).
One way to think about it is to consider your own position: presumably you have a reason for eating the way you do and one of them may be health-related. How do you feel on your diet? I'd honestly have to describe myself as an ideological vegetarian but I would add that I've been tons healthier since becoming vegetarian (20 odd years ago) than I was as a meat-eating child. I am also concerned that my choice to have children doesn't create further ecological burden.
Ultimately it's up to you. You could give him a supplement if you feel the need. Bear in mind there are many toddlers who eat a very very limited range of food (pasta and pesto only!) and they survive beautifully so don't get stressed about it! But, who can tell a mother not to worry, eh?!
