Many of the stores with lumber also have a saw area set up so you can cut the pieces to size. I've used them at Homes Depot and Lowes.
Can you use the bed without the footboard? Sounds like you bought a fancy Victorian thing that probably originally used a different kind of wire spring format. I know what you're describing with the slats - I have beds here that have those slats (only one is set up but not in use at the moment).
There's something to be said for the ubiquitous adjustable steel frame that can go from twin out to queen and has sturdy castors. I have my box spring and mattress on one of those and the headboard of the Victorian bed leans against the wall and the bed is in front of it (not so close that I bang the headboard into the wall when I move around). I don't use the footboard, it is stacked in front of the headboard between it and the bed to keep it out of my way.
Box is ready to go. I had to get out a new roll of tape and was disappointed to find that my sturdy Uline tape has a cheaper thinner packing tape and that's what Amazon had for sale. Bait and switch, too late to return it. There will be a review posted making note of this.
Picked up the yarn - a tiny bag when it comes to it, but the offering party was there and came out to apologize (she forgot to put it on the porch this morning so it was two trips). Seems she taught art for years and is planning to move in the new year and will have a lot of other stuff to list. I told her about the place for donations to local art teachers and she's going to check them out next time they're open.