Yes that’s a good idea. Maybe I’m thinking of it the wrong way round and trying to avoid triggering when what I need to do is help build self esteem up?
The reality is you can't avoid the triggers because it's every day life, it's much better to help kids learn how to know they're being triggered and help them cope with that.
In saying that I wonder if he's projecting his own feelings onto other objects? That can be a safer way of expressing feelings than owning them eg I don't know what to do with this feeling (or it's not safe for me to have feelings) so if it's teddy feeling lonely or scared that's ok. I think showing him how we care for someone who is upset, lonely or scared can reassure him that when he feels like that he too will be taken care of. You can extend that by wondering aloud whether he's ever felt that way and asking him what might have helped and doing that with him.
When kids have very early trauma experiences they can detach from their feelings as a form of protection, it becomes safer to ascribe those feelings to other objects or push them down entirely. I used to do games like show me your happy, sad, angry face while making extreme faces for each emotion, or we'd write stories and make feelings faces,
Depending on the long term plan (ie are they looking at permanence planning etc) doing work on the different types of relationships and how they grow and change might help because he may well move on from you at some point and feel rejected or replaced. He may be trying to communicate with you how unsettled and uncertain he feels which is perfectly reasonable given his situation, so some life story work around what's happened so far and what might come next could be helpful.
Foster carers have such a fine line to tread, but try not to avoid tackling his feelings in ways he can cope with.