Okay update bc my problem is solved, so for somebody asking himself the same question, here's what I did :
I created a sprite (just a dot) who is my avatar (only for this room).
In the case next to him, another same dot but it is an item.
The player just have to press -> to get the item, and I attached a dialogue to this tiny item dot + a page break and an exit to the next room !
Visually it's like a "..." so it's not really invasive in my landscape.
I placed tiles with wall all around those 2 boxes so my avatar can only go on the item.