Oh wow, I’m dealing with something similar! I accidentally deleted some DMs last week and I’ve been frantically googling how to get them back. 
I tried that Instagram Data Download thing that everyone mentions, but… did it actually work for you? I’m scared to try it because I read somewhere that it only shows messages that are still on their servers, not the deleted ones. Is that true?
And about those monitoring apps - I keep seeing ads for them but I’m really nervous. Do you actually need to root or jailbreak your phone for those? I definitely don’t want to brick my phone or void the warranty. Plus, is it even legal to install something like that?
The asking the other person idea seems like the safest bet, but it’s kind of embarrassing to admit I deleted everything by accident. Have you tried checking if maybe there’s something in your phone’s notification history? I heard that sometimes works but I’m not sure how to even find that.
This whole thing is making me realize I should probably start taking screenshots of important conversations… but that’s not helping us now, right? 