You won't be able to use a DS screen at all (they're specially designed for the DS, have a weird resolution and cannot support analogue composite input without a conversion board).
However, you can get away with using a stock LCD and driver board, the kind they usually put into rear-view camera displays. I've got mine coming in (for a SEGA Nomad TFT screen mod actually, but I'll hook it up to my Pi nonetheless) soon from aliexpress (although if you can find one elsewhere or use the faster shipping, I advise you to as the shipping isn't so great).
You can use pretty much any size screen, granted it supports composite input, but this is what I'm getting
and it's probably the cheapest you'll get them right now, unless you live in China and can order from Taobao.
I'm certain this same screen has been used for a Pi-in-a-GameBoy mod.
The driver board is necessary. You'll need to power it as well and connect the composite connection. There are usually some button controls to change the brightness or turn off the screen. You won't be able to get HDMI output on one of these screens unless you buy something expensive, or buy one of the more expensive screens with VGA input and use an adapter.
I don't know what size screen you need, but even something like this might work.
If you don't mind spending $60-90, some of these look nice and support HDMI:
8" with HDMI/AV/VGA
8" with AV/VGA
Another 8" with HDMI/AV/VGA
Search around eBay for things like "hdmi lcd panel" and see what you can find, there are also some 6" LCDs with HDMI inputs and there's this monster
of a driver board that supports a LOT of LCD panels.