Thank you for the inquiry and I’ll be happy to help! We have plenty of customers that order a firm and less expensive mattress and place either a 2" or 3" Talalay topper on it, and this provides the plushness and feel of a $2,000 mattress. I cannot attest specifically to the longevity of the Ikea mattress you have now, but according to the Ikea website, the mattress is made of the following:
Ticking: 64 % cotton, 36 % polyester
Ticking: 50 % polyester, 50 % viscose/rayon
Ticking: 64 % polyester, 36 % cotton
Comforter filling/ Part 3: Polyester/viscose (rayon) fiber wadding
Lining/ Part 04: Non-woven polypropylene
Part 05: High-resilience polyurethane foam (cold foam) 2.2 lb/cu.ft.
Part 06: Polyurethane foam 1.7 lb/cu.ft.
As such, this mattress may last anywhere from a couple of years to over 5 years, and I can’t say in advance which will be the case for you. With all that said, I think it would be a great idea to get a 2" or 3" Talalay topper to put on the mattress you have now. If you try this and it doesn’t work for you, you could always get two more latex layers and integrate the Talalay layer into a DIY all-latex mattress. Once you get three different latex layers within a zippered removable cover, you would have the option to unzip the cover and rearrange the layers to make it firmer, or you could replace a layer if you decide it needs to be softer.
Please keep the following in mind when choosing a thickness for your topper: A 2" topper will make a noticeable difference but, depending on how much you want to change the feel of your mattress, may still leave something to be desired. The 3" topper will change the feel of your mattress the most, and if that’s the change that you’re looking for then this would be the best bet. The best way to summarize it would be to say that a 2" topper will make the mattress feel moderately softer and the 3" topper will make the mattress feel much softer.
Both the thickness and the density make a difference when choosing a topper. Ultimately, how you make your decision will depend on the following: how firm your mattress is now; how much softer you want your mattress to be; your height, body weight, and sleeping preference (For example, if you weigh more than about 250 lbs I would recommend a medium topper; if you weighed more than 250 lbs and bought a soft topper, you would likely bottom out and sink right through the topper to the firm mattress that you’re trying to move away from). Based on the information you’ve provided, either a super-soft or soft Talalay topper would be just fine. Between the two firmnesses, I’d recommend the soft over the super soft and this is for a few reasons. Super soft toppers tend to break down sooner than normal, and that topper may last only a couple of years. Additionally, the super soft topper may be too soft for a stomach sleeper, so it may lead to lower back aches for the nights when you sleep on your stomach.