Hi mattressmatty, and welcome to the Mattress Underground 
Glad to hear you love your current mattress…and I can understand why you want to get ‘the same mattress only larger’ since you are so happy with it! It’s unfortunate this specific model has been discontinued, making it a bit tricky to replace.
As you may know, any mattress you find ideal will be based on your Stats (height, BMI, sleeping position(s) and any underlying health conditions) and your PPP (Posture & alignment, Pressure relief, and Personal preferences).
Though Sealy mattresses are popular with many consumers, like many of the ‘big brands’ they are not very transparent on the materials and densities of their components, as the memory and gel foams are proprietary formulas. This makes it almost impossible to assess how suitable and durable the foams may be for any sleeper - and making it harder to find a ‘similar’ feel in a new mattress.
You may want to take a look at the Mattress Specifications You Need To Know and see how they compare to the Mattress Durability Guidelines to get an idea of different mattress materials and their durability.
We suggest any foam in a potential mattress has no more than an inch or so of lower grade foams (for memory foam no lower than 4 lbs/cuft for normal range weights, and 5lbs/cuft for higher range weights) and if polyfoam is used, with at least 1.8 lbs/cuft density, just to ensure you have support. If the memory foam is insufficiently dense, or made of inexpensive fillers, it can develop ‘ridges’ and ‘valleys’ that can cause aches, pains and even alignment issues, and this is increased for sleepers with higher BMIs.
For a foam hybrid mattress, you might want to take a look at the offerings of the Trusted Members of the site; Bay Bed & Mattress has several polyfoam hybrids, while Fox Mattress has a wide variety of memory foam, polyfoam and gel foam hybrids, as does Mattress To Go, Texas Mattress Makers and Beloit, among others. In many cases, as these manufacturers have many years of experience in matching sleepers to their ideal beds, they may be able to replicate the ‘feel’ of your Sealy mattress as much as possible. I wish you success in finding a new better and larger mattress that surpasses the satisfaction you had with your Sealy!
~ Basilio