Hi Elisam and welcome to the Mattress Underground 
Sorry to hear your Berkeley Ergonomics bed is causing you so many issues….as you probably know, any mattress you and your husband find ideal 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 both have lower BMIs, you should have far more options in sleep solutions as proper support should not be an issue with any good quality bed. As you can see comparing the the Mattress Specifications You Need To Know to the Mattress Durability Guidelines, latex is one of the most durable - and breathable - materials you can have in a mattress. This of course doesn’t mean you can’t still feel ‘hot’!
Since you are feeling aches and pain with a plush comfort layer, but your husbands firm side is worse, I’m wondering if one issue may be that you are sinking into the 2" top layer and bottoming out on the layer below. Another factor may the the type of latex - Talalay latex rubber is ‘bouncier’ than Dunlop (the common comparison is the difference between angel food cake and pound cake). If at all possible, you might want to try a few different firmnessses, like a more medium-firm, of both types to see how they feel for you, as this may solve your dilemma.
Remember, no one can decide on what’s best for you and your husband except the two of you. For your body profiles, it’s really as matter of preference what comfort levels you sleep on…asides from the aforementioned ‘sinking in’ (more likely with a thicker plush comfort layer) it depends on how you feel on various firmnesses. With an 8" latex mattress, a topper of an inch or 2 in the correct firmness could allow you to ‘rescue’ your BE mattress, but it may take some trial and error to finds the right fit, which is why if possible, testing some mattresses in local showrooms could help solve the puzzle. Likewise with a hybrid of different type of sleep solution - it may or may not be comfortable for you both, and as you say, replacing your BE may be a little drastic. Since you are having issues sleeping hot, you also might want to consider a cover of wool, bamboo, or coconut coir, as this would provide an additional breathable layer between you and the mattress.
If you are considering online ordering, many the Trusted Members of the site have toppers and replacement latex layers of both types, and various firmnesses…giving any of these your Stats, PPP and mattress history, and the issues you are having, will allow them to provide some possible solutions. Unlike, for example memory foam, any latex you find in a store, once you match the comfort level and support level you need, will be durable for many years…the hard part is really matching those for you both.
It does seem like a little tweaking/adjustment of your present mattress could resolve your discomfort without a costly bed replacement; I certainly wish you success! Please let us know how it works out!
~ Basilio