Hi Gail1 and welcome to the Mattress Underground 
Sorry to hear you are not enjoying sleeping on your Serta, you aren’t alone in your views…many of the ‘big brand’ mattresses have a maximum of hype and PR but virtually no info on their materials and components, and many consumers find them to wear prematurely causing divots and ridges and sagging from the insufficiently dense foam. This can cause muscles aches and pains, as you have found, and even alignment issues.
As you may know, any mattress you choose will be based on your Stats (height, BMI, sleeping position(s) and any underlying health conditions) - thanks for providing those! - and your PPP ( Posture & alignment, Pressure relief, and Personal preferences). As you can see comparing the Mattress Specifications You Need To Know](Mattress specifications you need to know) to the Mattress Durability Guidelines, latex is one of the most durable mattress materials you can find, and a well made latex mattress could last for many years.
It’s good that your higher-BMI partner can ‘sleep on anything’, so you have more options for a compatible mattress with your lower BMI. You say you prefer a ‘medium to soft’ bed but don’t want to ‘sink in’, and correctly are looking for support as well. Mattress buying is an extremely subjective experience, so you will want to keep in mind a too-soft comfort layer may allow you to ‘bottom out’ on the firmer layer(s) below, which can also cause muscle and pressure point pain. The mattresses you listed are all considered somewhat ‘premium’ or ‘luxury’ brands and can come with a higher price point; only you and your partner can decide if it’s worth the extra cost. Looking at the listed mattresses:
Pikes Mattress Charles Franklin II:
Holland Springs
Resolve Firm Foam
Supple endurance foam
micro coils
latex foam
memory foam
As they do not list their mattress online, and provide customized mattresses, there’s a bit of missing info for this…there are no heights for the layers, or density for Andy of the foam, which tends to throw red flags up; terms like ‘supple endurance foam’ and resolve firm foam’ don’t really say anything and as proprietary mattress foam formulations there’s no real way to assess the suitability or durability for any sleeper. If you enjoy the feel, accept the higher price and they have good exchange/return policies, you may find this a very comfortable option, but the sparse details would signal a good bit of caution.
Bowles Catalina Mattress:
16.5"
1 1/2" foam quilted cover
2" 7 zoned ‘3.3 lb/cuft’ latex
1" 3lb/cuft ‘active response foam’
2.5" 17 gauge micro quad coil
1/2" 4lb/cuft gel infused memory foam
8" tri-zone quad coil support
1" 1.8lb/cuft firm base foam
This is a higher-profile mattress, and also has both microcoils and a pocketed coil support, which have a very specific feel that some consumers find to be too much support, but , like the height, is a matter of preference. Zoned latex is also popular with many sleepers, and the foams appear to have good enough density for your partner so that they do not wear out too soon.
Aireloom Luxetop M2 Plush
15.5"
Tencel silk/wool/graphite visco foam padded
cover
Celsion latex comfort layer
19 gauge microcoils 4000+ count
Airelux foam
15 gauge pocket coils with edge support
Aireloom produces quality mattresses, but again, without heights of the specific layers, and foam densitities it’s difficult to assess either suitability or durability. Many consumers enjoy the Luxetop M2, but again ‘your mileage may vary’ (thanks @BillyIdol for your feedback on the Aireloom!). Opinions on mattresses, like reviews, have limited usefulness for consumers: a sleeper with your same Stats and sleep profile may find a specific mattress too soft where you find it too firm. The important thing in your case is to make sure any mattress you buy has a good warranty & return policy, especially if the mattress is not as transparent in their components and materials…for the premium price you don’t want to find, months down the line that it’s not compatible and be stuck with it.
Of course in person testing is best, but if you are considering online ordering, you might want to take a look at the offerings of the Trusted Members of the site, who all offer quality sleep solutions that are transparent in their materials and components, and offer great customer support and generous exchange and return policies; Many of these carry latex hybrid mattresses similar to those you have tried, at a variety of firmnesses and price points.
Hopefully others in the forum community can chime in on their ‘hands on’ experiences with the mattresses you listed as well. I wish you success in your mattress search! Please feel free to drop in and share your experience with your new mattress once you have had some time with it too!
~ Basilio