Handhelds are awesome!
I'd say the PSP 3000, Nintendo DS/ 3DS, or steam-deck, however, it depends on what you're going for.
PSP is awesome if you want that sleek, pocket-size, multimedia device (you can even connect it to the TV). But if you want Nintendo stuff, I'd say a 3DS because it plays BOTH Nintendo DS and Nintendo 3DS games. Soft modding them opens up a huge library.
The steam-deck is like a handheld PC, though, not pocket-sized, I'd say it's worth it if you already have a big steam library.
Overall, if you really want a switch, you should totally save up for it
. Though keep in mind, outside of a few free-to-play games like Fall Guys or Fortnite, almost all major titles (like Minecraft, Mario, Smash, etc.) require a continuous payment for a Nintendo Online subscription (depends on what plan you get, but it can be a total hassle to keep re-uping every few months). But for modding you'll have a blast with the PSP/DS/3DS