How to stiffen up a daybed for adult use?  That is today's question, Tinkerers, haha.   I am renting an efficiency apartment temporarily (3rd floor of an old house), and I got a great deal ($75) on an '80s sold brass daybed.  (Yes, I am the USA's sole market for brass beds nowadays, lol.  I am the person who scored two gorgeous ones with onyx on them and posted pics last summer.)   This daybed even has the popup trundle unit.  I am contemplating taking this daybed to the efficiency apt because 1) It won't take up the whole room like a queen bed will, and 2) I don't think I can get the queen bed headboard up the stairs by myself, and I am absolutely sure that the queen 1-piece box spring won't go there, and I suspect that the queen mattress might not bend enough to go there, either.

So, I have this daybed, but it has those spring units and I think that they sag and flex and bounce too much for my tastes.   (Oak floor hardness is close to my perference, lol.)  Some of the modern daybeds I looked at have a wire grid and strap steel and angle steel mattress support that has no springs, and I like the way that feels with a good firm Bonnell spring mattress on it.   Are those wire grid things sold separately, and where? 

I suppose another thing that might work, for the upper mattress, width of daybed permitting, is two twin bed rails with a bunkie board or a slat kit and a good firm mattress on top of that.  But then how do you make the firmness of the trundle match?

Daybeds were all the rage in the '80s. and adults slept on them.  So, what type of foundation did they use back then?  The bed rails + slats?

I have to buy one or more twin mattresses for this, so I am looking to get the most bang for my buck and not buy costly parts if cheap ones will do.

One thing that I am tempted to try is get two twin slat things from Ikea and wire them over the spring units of the trundle unit and the main bed.  I'm not sure how well that would work, though.  Any experience with those?  They are sold as bunkie boards and as supports for foam mattresses.

Thanks.  I hope to get some ideas.   :-)