Hi MatRest,
Thanks for taking the time to share your comments and pictures … I appreciate it 
There isn’t any way to quantify your questions about “how long will this mattress last” because there are too many variables involved but all of them are in a very low quality range so for an adult it could vary from months in some cases to a few years in others (assuming they are comfortable and are a good match in terms of PPP in the first place). In most cases the best you can do is look at the construction of each mattress and look for any obvious weak links and make an “informed judgement” that “this mattress” will likely last longer than “that mattress” but it’s not possible to put a specific number of years on a mattress because it depends on how long it takes cross the thresholds from sleeping well on a mattress to “sleeping OK” to “tolerating a mattress” to finally deciding to replace it and this can vary widely between people. You can read about some of the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here and the posts it links to.
Ikea also doesn’t provide all the specs for any of the mattresses you mentioned (see this article) so it’s not really possible to make any particularly meaningful comments about them but I can make a few based on the information they do provide and I would be very hesitant to purchase any of them.
SULTAN HURVA:
I would make sure that it has at least 390 coils in a queen size Bonnell coil. If it has less than this (or if there isn’t a good insulator as you discovered) I wouldn’t buy it because it wouldn’t provide even support and the chances of it becoming lumpy fairly quickly as the foam sinks into the coils would be much too high. The innerspring is 5" tall so if the polyfoam layer is 3/4" then the rest of the 2" comfort layer would be synthetic fiber. With the 1.5 lb polyfoam and fiber and most likely a low coil count this would be a mattress that I would generally only consider as a guest bed or for a child. If it was being used for a child then it would probably be reasonable to expect it to last while they were younger but once they start to grow larger or reach their preteen years then it probably wouldn’t be suitable any longer although it could still make a good “base mattress” for a topper.
This would last longer than a similar mattress that didn’t have an insulator to keep the padding materials from sinking into the coils and getting lumpy and uncomfortable.
In most cases the springs aren’t the weakest link in a mattress no and the foams above them will usually break down before the springs lose their temper (assuming that the coils are tempured) but with thinner layers of padding the springs will be compressed more so they will be less durable than if there were thicker layers above them so their gauge and coil count would be a little more important. The bigger issue with Bonnell coils (outside of breaking) would be with the springs developing noises or with the springs coming through thinner layers of padding above them.
Ikea ships most of their mattresses compressed and to do this they need to remove any border wire in their innersprings so without this or a firmer foam “tub” there would be little edge support and again this could become a durability issue if you sit on the edge of the mattress on a regular basis.
SULTAN HANESTAD:
This mattress only has about an inch and a half of padding (lower density polyfoam and polyester fiber) over the 7" pocket coils. A pocket coil would be less durable than the Bonnell coil in the previous mattress because the coils aren’t linked together to “share the load” and this is also a lower coil count than I would tend to look at in a pocket coil mattress. With a thinner layer of padding than the Hallen the coils themselves would be doing more of the compressing and if they are softer than the foam in the Hallen this would account for the difference in feel.
SULTAN HALLEN:
This mattress has about 2.5" of padding (the thicker layer of lower density polyfoam and polyester fiber) over the springs so the foam would be doing more of the compressing than in the Hanestad which is probably the reason it felt firmer and more “supportive” than the Hanestad. Again though … this is a lower coil count than I would tend to consider in a pocket coil mattress. The thicker padding compared to the Hallen would also make it less durable (more “soft stuff” on top to soften and break down over time) so it may have more of a tendency to develop soft spots or impressions over time.
[quote]The IKEA website says here that the foam on top is “High Resilience”, so maybe that explains the feeling of support. This foam looks a little bit thicker too.
Question: Elsewhere on this site, "High Density foam is described as starting around a density of 1.8 lb/cu.ft, and “High Resilience” foam is a notch above, starting at 2.5 lbs. IKEA says that this “HR” foam is 1.5 lb/cu.ft. How can that be? Creative license? A Swedish pound? I guess the HR term isn’t controlled?[/quote]
1.5 lb polyfoam isn’t HR polyfoam so this is “creative license”. The foam in the Hallen could be a higher performance polyfoam that has a higher resilience than the same density polyfoam used in the Hanestad or in the Hurva (which would also make it more costly) but it would be in a similar durability range to other 1.5 lb foams and high performance polyfoam isn’t the same as HR polyfoam even if it does have a higher resilience than conventional polyfoam. Resilience is the percentage rebound when a ball is dropped on a material and higher resilience means that the ball will bounce higher. To qualify as actual HR polyfoam a foam would need to be 2.5 lb density, have a compression modulus or 2.4 or higher, and have a resilience of 60%.
[quote]If I shop at IKEA, I’m trying to choose between a “firm” (at first) spring mattress in the HURVA, and a “giving” mattress in the HALLEN. All the while trying to correlate the effects of a ~135 lb adult to those of a 40 lb child. The mattress will be placed on a very solid built-up plywood base as part of an older wooden bed.
Sure, the child will grow, but how long before their weight is too much for a low-end IKEA spring? And if they sleep on their stomach sometimes, will that cause a problem?[/quote]
If I had to choose between these mattresses for a child (although I would hesitate to choose any of them) I would lean towards the Hurva with the Bonnell coil which would likely be firmer and more suitable for a child and also more durable and could also make a good “base mattress” for a topper so you could extend its useful life when they get older and heavier and begin to develop and need some additional padding and pressure relief in their mattress .
Phoenix