What challenges? It’s easy and fun, although you might hit densities that don’t quite work out for you but most vendors will exchange the foam for you (you pay shipping costs). Chances are very high you will hit it right. I’ll speak for myself (recommend a Forum Search on my posts too) - I built my own and hit it out of the ballpark plus saved a lot of money - (3) 3" slabs of talatech latex zipped up into a cotton stretchy encasement placed on a solid top box. Firm on the bottom, 36ILD, medium over that, 28Ild, plush topper, 19ILD. Got a 2" 14 ILD coming in today to really kick it up a notch. 
Pix -https://forum.mattressunderground.com/t/mattress-cover