We've just purchased a secondhand bell tent that comes with a groundsheet but no additional carpet/rug/matting...
We're 'occasional campers' - a few long weekends each year - 2 adults and 2 young children so lightish traffic but high potential for mess!
I've looked at coir mats (bulky, expensive, heavy), jute mats (possibly too lightweight looking at photos of it not sitting flat/is it worth it?), recycled plastic mats (leaning towards this), or just buying rectangular outdoor rugs (look attractive in photos but would they be practical?) or even picnic blankets (too lightweight/a trip hazard?).
What do experienced bell tent campers recommend?