I'm playing a Feypact Warlock Catfolk who summons Grandmas (cat ladies). I'm satirizing the Pet Class, flipping the script, where the pet summons owners. Anyway, my DM allowed me to summon an "Animated Armor" as my special familiar or "owner" by wearing a collar that uses an attunement slot. I call her Babushka Yaga. We're 12th Level now and we've come across the same issue you're having with "dud" magic items. As a result, Babushka wears a Winter Cloak (like the boots), carries around a cursed great axe, and wields a magic scimitar (Moon Blade).
Pretty much the only time she fights is when she's making an Attack of Opportunity. Since she has a magic weapon her AoO's can be a credible threat but even then it's not too dangerous because the Prof bonus doesn't scale so her total bonus to hit is only +5. Even with Bounded Accuracy it doesn't make too much of a difference. And that's what you'll discover - giving a magic dagger to a Sprite isn't going to be a game breaking combo. The Paladin's "Find Steed" spell is far superior than the Warlock class ability even after doling out magic weapons. When you're fighting Frost Giants and Ice Devils a 33hp Animated Armor gets pulverized in the blink of an eye. Don't think a Sprite will last much longer. If anything, handing it a dagger is like sending it into the pits of the Colosseum. Expect it to die.