Hi sleepaid,
Welcome to the community. Sorry to hear about your journey and unsuccessful relationship with the last several mattresses.
I am 6’ 220 and I sleep on the Plank Luxe firmer side, my wife is 5’4 135 and she is a side sleeper too as I am and for us, the plank has been exceptional over the past 2.5 years. One thing that you will find it that the is not just one type or style mattress that will work for you. But there are certain ones that definitely will not.
One thing about the firmness of the Plank/Plank Luxe Mattress, is there is not much contouring going on. You sleep very flat on the mattress, for some this is ideal, and others, well the contouring is critical. While it is not clear if you are a back, side, stomach or combo sleeper, if a side sleeper, the wrong pillow will definitely cause should pain. The topper likely would have reduced some of the shoulder pain, reducing the pressure, but a loftier pillow would non the less be suggested for side sleeping.
Taking an overall more broad view of your history some things come to mind. Before I go there, remember, your foundation and pillow are equally important to the mattress you select. A poor foundation and the wrong pillow as mentioned, can cause issues from the neck to your legs.
When it comes to your issues, the fact that you have low back pain when you wake up, but seems to improve during the day, tells us that your lumbar spine is probably not being properly supported during sleep. As mentioned, the Plank may have been too firm with nothing filling the void under your back or above your hip area when sleeping. If the mattress was too soft, which could have been the issue with the Helix Midnight Elite, your hips may have been sinking too much (although the Helix Midnight Elite did have the option of the ergo align to counter those hips from sinking, and the new Helix Elite Series is a great improvement for this situation. Additionally, if the Elite series had been purchased at an authorized independent dealer, you could have simply exchanged the Midnight layer, for a Twilight layer. Water under the bridge now.
The fact that it gets better throughout the day implies it’s a positional/postural problem while you’re sleeping.
Your lower leg issues are likely a result of some sort of nerve compression common with lumbar stenosis, and muscular tension due to misalignment. This will almost always become worse with too soft of a mattress. The Helix Midnight is not a particularly hot mattress to sleep on, but if your alignment was off, causing pain and inflammation, or nerves being over stimulated it may feel more like heat rather than the mattress being hot.
The shoulder pain as I mentioned, is likely the combination of a firm mattress, possibly in combination with a side sleeper, and not the right pillow.
I feel like there is a little too much mattress guessing going on, and not enough professional advice.
At this point a mattress that offers contouring and lumbar support, combined with an appropriate pillow is the direction you should be heading. I would like to know what foundation you have too, as the wrong foundation for a mattress is a recipe for pain. Even Keetsa had requirements for their mattresses where they want the slats to be no more than 2" wide and less then 4" spaced (which I think is too much, keep it under 3" spaced).
A conversation with @BackScience would be a good start, as their backscience 2 mattress offers a great balance of support and comfort, along with modifiable lumbar support.
Trying a mattress in a store for a half hour is only going to suggest if a mattress is too soft. Soft presents itself rather quickly. On the other hand, firm may not, actually firm will usually feel great, but it is how you feel after a month or so on the mattress system is what tells the story. I dont think Saatva is going to be an answer here either, the Rx is around a 3-4/10 which may be too drastic of a change.
The back science 2 or maybe 3 offers a medium-firm medium feel with superior lumbar support, where the 3 is a medium feel with enhanced lumbar support. The fact that they have a 365 day trial, modifiable mattress, is a big plus.
If you are in NJ, a trip to @ShovlinMattress in Fanwood, near Scotch Plains and Westfield, would be a place to visit to experience a custom designed mattress to address each area of your body. Like the folks at Back Science, Shovlin have been in the business for over 30 years, customizing mattresses.
I think it is time for a pause and collaborate with someone who is going to listen to your symptoms and come up with a plan to really dig in and solve the problem. I am encouraged that the latex topper helped with the Plank mattress, it may not have been the right thickness and ILD to completely solve the problem, but it does appear you were on the right track.
I expect @BackScience and @ShovlinMattress will chime in and offer some advice (assuming you are live in NJ) If not, there are some other suggestions up our sleeves here at TMU to help you along.
All the best,
Maverick