|>>|| No. 2841
It doesn't have to be nearly a grand as >>2838 mentions, but a good bed costs money. You can build your own if you're handy around wood, but if you're buying one anything which comes as a kit with fancy nuts and bolts to screw it together is, very likely, a bunch of tosh. The metal frame shown in the picture, for example, looks exactly like the kind of trim you find on a tube framed bit of cheapo nonesense.
If you don't want to go DIY, find a (semi-)local bed maker and get something that's made of squares and screws together with plain wood screws. Then apply >>2839 and reinforce it; the entire bed should, if at all, move and flex as a single unit. Any play in the component parts will get stressed incessantly as you toss and turn during sleep. When reinforcing, bear in mind that you put more pressure on the bed around your hips and mid-torso than your head or feet both when sleeping in it and when falling into bed or sitting down/up on it, so the centre area is particularly important to reinforce.
I'm no Big Bear at *mumble* over 15st, but even I learned that slats are wear parts. It does depend on your mattress and how well it spreads your weight across them but having a half dozen or so spare at all times is a god sent. Check your bed every 3 months or so to replace slats that appear less than perfect. You can even do a rotation, move slats from near the end of your bed towards the centre and get some more use out of the centre ones near your feet for example.