I'm wondering what the OP went with. I know it's a necro thread but for people who may come across it quite a few suggestions of using a plywood base under the mattress. Probably better not to, the type of mattresses that usually require a platform bed like latex, memory foam etc need to breathe. It may not happen right away but having a closed off surface like plywood can lead to mold/mildew. Slatted or some variation are a better answer.
Those metal frames that come folded up seem to be a mixed bag. Some say they work great, quite a few report issues of squeaking from the bolts and things between the frame members, others have said they're not all that big and yet bent the side of the frame when sitting on the edge of the bed. They usually say they hold some crazy amount like 1400lbs or something and I'm sure they do. If the load is evenly distributed. Eggs on end or paper tubes with a nice level fully distributed load can carry a shit ton of weight but not once it's off balance or the weight is localized to the side rail.
I've still got to get one made myself, definitely need to light a fire under my ass and get it done this spring/summer. Won't be anything super sexy like walnut or maple, even living in the boonies it's scarce to find affordable rough cut hardwood. Shit costs a small fortune and nowhere local. The few mills I've hit up aren't interested and basically point me back to the hobby packs at the borgs. So the challenge will be to use cheap ass pine construction lumber and have it come out looking halfassed decent. lol. Should be stronger than whatever I can buy for reasonable prices and likely cost a bit less.
It'll be some work but I think it'll be worth it doing it right. So many diy sites got people smacking it together with pocket hole screws or just screwing shit together face to face so the fastener's trying to support all the weight. Not to mention designs that might be fine for a flower bed or fast/nasty outdoor project but that doesn't take into account racking forces of a bed. Not that I see much extracurricular action these days, I just don't want to wake up with my ass on the floor lmao.