Hi Starálfur,
I think most of your questions are answered in the first post of this topic..
A latex mattress generally does best on a slatted platform bed or on a firm non flexing foundation (not a box spring which has springs inside it) that have gaps between the slats of about 3" or less.
You will rarely see box springs any more outside of some smaller manufacturers and most of the mattress support systems that are sold with mattresses today are foundations (not box springs) that have either limited or no flex and don’t have springs inside them.
If a bedframe is meant to be used with a foundation and has good center support to the floor then it’s just a matter of using a suitable foundation (again with slats that are less than 3" apart) on top of the bedframe and under the mattress
If you wish to use the bedframe without a foundation then you would need to add more slats to the bedframe to properly support the mattress so that the distance between the slats was less than 3".
Phoenix