Floor leveling in an old barn

Hello, thanks for thinking along. Photos are difficult right now, I'm not on site. I have made mortar bags several times, it's quite tedious (especially in winter). Do you have any recommendations on which battens or floorboard cross-sections would be best and what spacing / spans would be appropriate for them? Devices up to max. 120 kg will be installed. Thanks!

Do you have any recommendations on which slat or plank cross-sections would be best and what spacing/span lengths are suitable? Devices up to a maximum of 120 kg will be placed on them.

Support beams 60 mm x 60 mm are fine, spacing maximum 45-50 cm, thickness of the planks (as the usable surface) at least 22 mm.

I have made mortar bags quite often, it's really tedious

but it does build muscles

With mortar bags you do better, especially since you have already done it once.

There is no adjustment range up to 11cm, so you need different sizes.

Ok, thanks! Last question: to make it as smooth as possible, is it better to use boards with tongue and groove? Or do I need expansion gaps across the surface? (the outside is clear)