How to combine sprites to create a seamless and efficient level

I am developping a 2D tile-based top-down game. It is currently instantiating square objects with a sprite renderer to procedurally generate the map.

Each floor and wall is a 1-unit wide object.

I have two issues with that:

1. The memory usage is quite high and it is not efficient (generating maps that are more than 300x300 become really slow)

2. There are lights glitches when I have multiple lights in the scene. The borders of the squares become visible as seen in the picture:

• Is it possible to combine all my static elements (floor and wall tiles) in a Mesh objects, or another adequate object for that?

• The floors items do not have colliders, as the walls have a box collider. Does it cause an issue?

• Maybe I could have a big "Floor" object, and putting on top of it a "Walls" objects containing all the walls with the corresponding colliders?