Use Friede and you already save one letter though it might carry religious overtones. Writing Fride might be ambiguous in spelling but as there's no "Fridde" it's not actually a problem. In any case the root is "Fried" (and yes belfries might have gotten their name from there) and you can be sure both Frieden and Friede are pronounced like that somewhere (over here it's Friedn and Friede), and as German spelling doesn't (officially) use apostrophes all over the place when spelling out contractions and everything writing Frid would be highly non-standard, but you'd definitely get away with it in a poem. Just don't show it to someone who studied Germanistik auf Lehramt.