Tony L
Administrator
@Tony L - I can't recall what base you said you're putting it on but pocket-spring matresses are best on a flat base rather than slatted (the pockets won't work well if there's nothing under them inbetween the slats). If you have a slatted base I can recommend buying some moderate thickness pegboard cut to the size of the bed frame and using that to create a flat base over the slats for the mattress to sit on. The holes in the pegboard also allow for some ventilation underneath the mattress.
Sleepeezee (the maker of the mattress I bought) say slat gaps up to 7cm are fine, and that’s what I have. It may actually work out less than that in practice as there is a central ‘north/south’ beam supporting slats either side, i.e. the central area is very well supported.