Hi suspent,
I would probably suggest first buying a mattress so that you can make sure that the support system you choose is suitable for the mattress. There is more about the types of foundations or support systems that are usually best with different types of mattresses in the foundation post here and the posts it links to.
My concern with the Malm bedframe would be that it doesn’t have center support to the floor under the steel center beam and I would want to check with the manufacturer of the mattress I purchased to make sure it meets their warranty criteria.
If you are looking at a slatted foundation or bedframe for a latex mattress then a rigid non flexing foundation or slatted bedframe would normally be the best choice and the distance between the slats should be a maximum of 3" and preferably less. If the support layer of your mattress is polyfoam (which would include most memory foam mattresses) then a little larger gaps would normally be fine (although less is still better) but I would always check with the manufacturer of the mattress you purchase to make sure a foundation or bedframe is suitable.
If you decide on one of their two flexible slat foundations then while they may provide even support and the gaps would probably be fine, I would also be aware that it may change the feel of the mattress compared to what you tested in a showroom if the mattress was on a rigid non flexing foundation or platform. Many memory foam mattress manufacturers also specify having a solid non flexing foundation or bedframe under their mattress so once again I would check with the manufacturer of your mattress to make sure that either one of these met the warranty criteria. I also don’t believe that either of them has any flex under the center beam which could mean that the center of the mattress may feel firmer than either side or you may feel a “ridge” in the center (depending on the type and thickness of your mattress). If you do choose one of these and it meets the criteria for the mattress you choose then the laxeby has a better support surface and also has the advantage of being adjustable under some areas of the body which can help to fine tune your mattress as long as the mattress was thin enough to feel the adjustments underneath it (and this would also depend on your weight).
Overall though … I would purchase the bedframe or foundation at the same time or after you purchased a mattress so you don’t have a bedframe or slat system that restricts your choice of mattresses and you can make sure that it’s a suitable choice.
If you decide on an innerspring then it would be even more important to make sure that your support system is approved by the mattress manufacturer and you may need smaller gaps than the Lade so that the springs aren’t over any gaps in the foundation or slat system and have good even support underneath them. In some cases an innerspring mattress may also have a box spring that is an integral part of the sleeping system.
In case you haven’t read it yet … the tutorial post here has all the basic information, steps, and guidelines that can help you make the best possible mattress choice … and know how to avoid the worst ones.
Phoenix