I think the middle size might be suitable for this. I will have to do some measurements to make sure and will let you know in a couple of hours when I have the time.

Sure thing, take your time! I'm still waiting for a new filament, so no rush. Also, I would like to mention that I have a Bambu A1 Mini, so I was thinking about printing shelf model called 160x100 (six of them - Lego train has length around 90 cm). For the wall I wanted to go with 8x8 model from A1 Mini. Also wanted to print six of those.

This will work with the 160x100mm variant, but there will be approximately a 5mm gap between the shelves. Due to a slight curvature around the edges, the gap will be slightly larger on the surface, roughly 2mm more. A bracket like the one found here (https://makerworld.com/en/models/171778?from=search#profileId-188576) or this top mount variant (https://makerworld.com/en/models/130958?from=search#profileId-142049) might be a better solution in this situation. The top mounting shelf's profile is not directly compatible with the A1 Mini, but the shelf itself can be scaled without any issues in Bambu Studio (make sure you only scale the X axis).