Hi ghiggz,
I’m sorry your Helix mattress didn’t work out as well as you had hoped for your prone sleeping posture. 
At least you did choose something with a good return policy.
Regarding the Winkbeds Plus, it has been discussed here previously, and the specifications are provided in this post. With your request for sleeping “on” the mattress versus “in”, you’d probably be more interested in their Firm option or the Plus. They rate their Firm actually a bit harder than the Plus model, so you may prefer that. I would definitely place a phone call with Winkbeds before making any decision to gather their opinion of which product they offer might potentially best suit your needs.
Regarding the Nest Bedding Latex Hybrid Firm, it uses the Leggett and Platt 5-zone Quantum Edge pocketed spring unit. The Winkbed uses a zoned pocketed spring unit with a polyfoam encasement edge system in the Firm and the Plus. On top of the Nest Bedding is 3" of firm Organic Dunlop latex, with wool and cotton quilted to the top panel. The Winkbed in the firm uses 1" of 1.5 lb 17 ILD polyfoam and 1" of 1.5 lb gel polyfoam at a 17 ILD, along with a micorcoil layer. So the padding layers between the two products are quite different.
The Nest Bedding Q3 Nest Bedding Latex Mattress comes as a component-style system and can be had as a firm/medium option. It uses Dunlop latex that can be has blended or organic certified. There is a 6" piece of firm Dunlop and a 3" piece of soft Dunlop. For the “firm” comfort, you’d arrange the product with the 6" firm layer over the 3" soft layer. For the “medium” comfort, you’d reverse the layering order.
As for the blended versus GOLS certified choice, most people that are looking for an “organic” mattress or materials are usually concerned more with “safety” than whether the materials have an actual organic certification and they usually aren’t aware that an organic certification isn’t the same thing as a safety certification. There is more information about the three different levels of organic certifications in post #2 here and some of the benefits of an organic certification in post #3 here and there is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here and more about some of the differences between organic and safety certifications in post #2 here and there are also some comments in post #42 here that can help you decide whether an organic certification is important to you for environmental, social, or personal reasons or whether a “safety” certification is enough.
As for the Saatva, they make quite a few different mattress models. Specifications for some of them are provided in the simplified choice thread here.
I hope that information helps you clarify the construction of the products in question.
Phoenix