I'd like to knock through an internal, 8cm-thick wall in order to install a door. The door will be sliding, and the sliding rail will be drilled into the wall above the opening.
I know lintels are mandatory for load bearing walls, but what about non load bearing ones? For only 8 cm thick walls, are they advisable? All of the concrete or brick lintels available in my nearest hardware stores are minimum 11cm thick, which means it'd overhang the opening by 1.5cm on each side -- which would make it look weird. I could potentially use Knauf's UA door lintels made from metal, but they're more designed for drywall.
Any advice or tips would be appreciated. I've attached a photo of the wall material and a partial floor plan.