BOF we bought the slats from here and DH did it. He's no good at DIY so it can't be that hard! He just screwed some bits of wood to the inside of the bed base and then we got the slats from the website made to measure and it fitted perfectly. It was I think around £150 or so for our king size bed.
I think try sell them separately. There's a French reclaim eBay shop that will manufacture a base for a bed, don't now how much though. That and the uncertain degree if squeak sent me to loaf for a repro version.
Yes, I've got an antique French king size bed and love it.
If it helps I bought mine at the french depot they have an ebay store. I went to their warehouse before buying just as I happen to be in the area and they have a huge warehouse full of amazing furniture and are alot cheaper than anywhere else I found.
I've just put in an offer on eBay for an antique French king size bed. It's got a lovely carved headboard, side rails and foot end. I love antiques but I've never owned an antique or vintage bed. Have I made a good choice? If my offer is accepted, it's going to be significantly cheaper than this reproduction that I've been seriously tempted to buy