Hi there. The iSeries 500 came out around 2017 and was actually called a "Cushion Firm," which is how some manufacturers at that time referred to a mattress that had somewhere between a Firm and Medium level of softness. The 500 was a quilted memory foam hybrid mattress with about 3.5" of memory foam right below the quilt, and a pocket spring support unit underneath. It was technically a tight top, but had a high profile at about 14" thick. It was discontinued about 2-3 years after it came out and is no longer available, but you can still see some information about it here: https://www.goodbed.com/mattress-model/serta-iseries-500-cushion-firm/

Since we haven't compiled a formal list of the most equivalent options for this particular mattress (if we had, you would see them on the link above), the first place I would look is our mattress search tool, which lets you filter the universe of available mattresses by whatever criteria you want. Applied to the details I provided about the iSeries 500, there are currently 64 models that are similar. You can see those here:

https://www.goodbed.com/mattress-models/?softness=5&softness=4&softness=3&surface-type=1&support-type=53&comfort-type=6&cushioning=2

Since this is quite a lot of options, I would focus on the ones from Serta, since those will be easiest to map to your existing model in terms of quality and feel. Currently, that narrows it down to these 13 options:

https://www.goodbed.com/mattress-models/?softness=5&softness=4&softness=3&surface-type=1&support-type=53&comfort-type=6&cushioning=2&b=serta

To cut this down further, in my opinion the Perfect Sleeper X options will definitely be the most comparable to the iSeries 500, especially the ones at Level 2 of the collection. Here are the 4 that I'd focus on:

1. https://www.goodbed.com/mattress-model/serta-perfect-sleeper-x-max-firm-pillow-top/
2. https://www.goodbed.com/mattress-model/serta-perfect-sleeper-x-max-medium/
3. https://www.goodbed.com/mattress-model/serta-perfect-sleeper-x-max-plush-pillow-top/
4. https://www.goodbed.com/mattress-model/serta-perfect-sleeper-x-lexton-medium-pillow-top/

All of these models share the same overall construction, are made with similar materials (including 2-3" of memory foam), have a softness level between Firm and Medium, and are very close in terms of their height. You can see all the details on how they stack up in this side-by-side comparison: https://www.goodbed.com/compare/?mod=serta-perfect-sleeper-x-max-firm-pillow-top&mod=serta-perfect-sleeper-x-max-medium&mod=serta-perfect-sleeper-x-max-plush-pillow-top&mod=serta-perfect-sleeper-x-lexton-medium-pillow-top

The last thing I'd mention is that all of the models above can be purchased online no matter where you live. However, if you'd prefer to purchase from a local retailer, this type of mattress may also be available in nearby stores as well. You can check our local mattress search tool to see if any of the stores in your area carry this brand or other products of this type: https://www.goodbed.com/mattress-brands/?surface-type=1&support-type=53&comfort-type=6

If the local search page guesses your location incorrectly, you can enter your correct zip code using the "Distance & Location" filter.

I hope that's helpful.