I’m a final year University student (5; 10", 160 lbs and back sleeper) in the UK and the single bed spring mattress in my accomodation this year is sagging in the lower back area. It seemed the most sensible option was to buy a relatively inexpensive topper as oppose to a new mattress to use this year as I’m not sure what bedding I will have next year.
A latex topper seemed the obvious choice, as I’ve had previous experience with both a memory foam mattress and a topper and they worked well besides the heat problem. From my reading, its seems a 2" or 3" of around 30 ILD would be ideal.
While there’s a large amount of brand suggestions both here and on other websites, all of these brands appear to be unavailable in the UK. The UK brand latex toppers I’ve found have few/no online reviews and are listed below:
Unfortunately I don’t have any knowledge about the UK market so I won’t be able to help with any specifics but I would read post #5 here (except replace the word “mattress” with the word “topper”).
If a mattress is still in very good condition and there are no visible impressions or sagging or soft spots in the mattress (particularly under the heavier parts of your body such as your hips/pelvis) and the only issue is that it is too firm then a topper can be a good option to add some additional softness and pressure relief although there is always some risk and uncertainty involved in adding a topper if you haven’t tested the combination in person because the mattress itself along with your own body type, sleeping position, and preferences can affect which specific topper would be a suitable choice on any specific mattress.
On the other hand … a topper is not a particularly effective way to “fix” a mattress that is already too soft or that has developed soft spots or sagging and at best it may provide a temporary or partial solution and at worst it can make some of the issues you are experiencing worse. If you add a firmer topper to a mattress that is too soft then the new comfort layer (the firmer topper) may end up being too firm to be comfortable for you to sleep on and the topper will usually still “bend” or compress into the layers underneath it that are softer or have developed soft spots or are sagging so you can end up with both comfort layers that are too firm and uncomfortable and support or transition layers underneath it (that were meant to be softer comfort layers) that are too soft to provide suitable support under the topper.
The most effective solution for a mattress that is too soft or has developed soft spots or is sagging is to first identify the layers that are the cause of the issue (usually the upper layers of the mattress) and then removing and replacing layers that are too thick/soft or that are sagging
There are also some suggestions in post #4 here that may be helpful for a mattress that is either too soft or has developed soft spots or visible impressions as well.
If you do decide to try a topper then knowing the materials that are in the topper is the best way to make apples to apples comparisons between toppers and is always much more important than the name of the manufacturer that made it.