Playing DS/3DS games: Should I get a second screen for my SD OLED or get an AYN Thor?

Got myself a Steam Deck OLED around 5 months ago and I'm super happy with it, amazing device. Now with the emulation options open to me, I got really excited and nostalgic for my DS and 3DS games... But running a dual screen game on one screen seems off to me.

Now, the AYN Thor seems like a wonderful solution.... But it's also very costly, and adding a second screen to my deck seems like a less elegant solution, but it might be plausible.

I'd love to hear your experiences, suggestions and takes on the each of the options, or even alternative solutions. Thanks!