Hi Pickles,
Some of the Amish manufacturers make some very good quality and value mattresses.There has been some good feedback about them in the forum (see this thread about Country Bedding as an example).
CertiPure can also be important as well but it’s a “safety” certification primarily (for VOC’s and harmful ingredients in the foam) and the quality of polyfoam and memory foam is expressed in density.
Having a two sided mattress is also a durability bonus and it can be especially important when there is polyfoam in the comfort layers. Many of the smaller manufacturers do this and if I was looking at a more traditional innerspring mattress I would certainly lean in that direction.
I think this can be a great idea. The latex topper will extend the life of the foams in the mattress (just like the ability to flip them) and with firmer mattresses this can be a great component system and has the flexibility to change or replace the topper down the road without having to change or replace the entire mattress.
The softness and thickness of the topper would depend on your body type, sleeping positions, and on how much soft foam was already on top of your mattress. The comfort layers in the mattress and the topper combined would become your comfort layer so thicker and softer layers in the mattress would lead to a thinner topper while very thin firm layers in the mattress could use a thicker topper. Since you are on the light side … softer latex would generally be the preference for most people. Side sleepers generally need thicker comfort layers than back sleepers and stomach sleepers need the firmest thinnest comfort layers of all the sleeping positions.
A good guideline would be 1" for “just a bit” more softness, 2" for a “little to a fair bit” and 3" for lots more softness although all of this of course is very subjective and will vary person to person. Keep in mind that the more soft foam you have in the top of your sleeping system (mattress and topper combined) that the further away you are from the support system and the more risk there may be for support and alignment issues. A good average guideline is about 2". The firmness would be dependent on your preferences but 19 ILD would probably be in the range for most at your body weight with some people maybe going a little firmer into the upper end of the “soft” range of about 24 ILD. Dunlop will feel a little firmer than Talalay in the same ILD because it gets firmer faster with compression than Talalay.
So it may be helpful to know the layering of the mattress you are considering and more about your sleeping positions and how the mattress feels without a topper (so you have a better sense of how much more softness you may need) before deciding on the specifics of a topper. There may be other manufactures near you that carry latex that you could test as well (if you let me know what city you’re in I’d be happy to let you know of any I’m aware of).
Overall though … a high quality two sided firm mattress with a high quality topper can make a good quality, flexible, and durable sleeping system IMO.
Phoenix