DIY Build Help

Hello everyone I’m looking into building a DIY mattress for my partner and me and I was hoping to get a little help. We’re fed up trying all the bed in a box stuff and we’re thinking we want to try building a latex hybrid. We tried one in a store yesterday and liked it pretty well (Berkeley Ergonomics Baltic IA soft which is basically a coil unit plus 2 inches of soft talalay with an added 1 inch talalay pillow top). We also tried their all latex bed but did not like the “dead” feel to it. The springs add some nice liveliness and responsiveness that we both like. The thing is, that mattress is pretty expensive and after doing research I know we could build something of comparable quality for far less money.

To start, I am male, 5’8, 160lbs mostly back but sometimes side sleeper and my partner is female 5’4, 150lbs all side sleeper.

One option I’m thinking might work would be a coil unit (probably the 8" L&P Bolsa unit which is supposed to be better for side sleepers) plus a 3" soft talalay layer, which is essentially what the mattress at the store was. I think we would want a stretchy cover for it but I’ve read elsewhere that those don’t work well for DIY builds with coil units. Is there any truth to this?

Another option would be the same coil unit, a 2" soft talalay layer, plus a 2" Serene Foam topper. I like this idea because we both like the feel of memory foam but it makes me too hot. My understanding is that Serene foam has a similar feel to memory foam but sleeps cooler. This build would (theoretically) have the nice responsiveness of latex mixed with some nice contouring.

I was also considering the Arizona Premium Ultimate Hybrid in plush but my concern is that the Combi-Zone coil unit would be too firm and that the cover wouldn’t be stretchy enough to get the true feel of the latex or be good for side sleeping. The advantage of going this route, however, is that it would likely be easier to return if we ultimately (pun intended!) don’t like it.

One more question I have is that I’m wondering if there is a need for a bottom layer of foam under the coils? I’ve seen mixed opinions on this and I’d rather not have one if it’s not needed to keep costs down but if it truly does offer benefit I have no problem throwing one in there.

Thank you all for reading and I appreciate any help and feedback you can offer.