Hi ron bruce,
Welcome back … it’s been a while 
The information in post #4 here should help you to assess the quality and durability of the materials and components in a mattress and the mattress “as a whole”.
There is also more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you make more meaningful quality/value comparisons between mattresses and there is more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of PPP in post #2 here that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for once you actually sleep on your mattress.
Novosbed, Memoryfoamcomfort, and some of the Ikea mattresses would make good quality/value choices that would certainly be worth considering but I’m not familiar with the specifics of the materials in the Jysk mattresses.
If the “foamshop” you are considering is Foam by Mail (FBM) then I would read this post and this post and this topic (about their polyfoam and sources) and this post (presumably from a past employee) before buying anything or considering them as a reliable supplier.
If you are attracted to the idea of designing and building your own DIY mattress out of separate components and a separate cover then the first place I would start is by reading option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
If you decide to take on the challenge then I would either use the specs (if they are available) of a mattress that you have tested and confirmed is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) as a reference point and try and “match” them as closely as possible or use a “bottom up” approach (see post #2 here).
I’m looking forward to finding out what you end up deciding and of course any comments or questions you may have along the way.
Phoenix