I would really appreciate your help on this matter, since I cannot find the information on my particular question online. So I have bought the bonnell based mattress in this category of products (not exactly this one; in my country there are few of them in the product line so mine is more expensive) Products - Discover Our Full Range Of Furniture And Homeware - IKEA .
I need a mattress for year, year and a half so I wanted to avoid bigger investment. The potential problem I am facing is my bed base which is really scarcely made: the gap between the slides is around 10 cm. By the looks of it I would say that his was made by some carpenter or so (I am renting the place so I don’t know). It is a pretty thick wood, but I am wondering can the gaps between the slides distort my mattress and should I go shopping for bed base to?
Depending upon the Bonnell spring being used the 4" gap could be a little wider than preferred. 3" would be better. Personally, if I were in your situation with the parameters you described, I would place a thinner sheet of plywood on top of the slat network. This would be less expensive that purchasing a foundation and would be a simple solution. I know the base wouldn’t be as breathable but for your timeframe it would be a simple fix. You may get some other ideas from other forum members as well.
I don’t know the specifics of your mattress or your bed base but for the few days that it will take you to buy some plywood I would probably put your mattress on the floor just out of caution.
Replacing the slats or adding to the slats you have so that you have a support system with more surface area and less distance between the slats certainly makes sense as well and would also be more breathable than a solid surface support system (see post #10 here).
Thanks for letting us know what you ended up deciding.