Obviously all these suggestions are prefaced with the caveat: Ask your voice teacher if you're ready for a particular role.
This said, you might want to look into some Falcon roles, which are ideally suited to mezzos making the transition to sopranos. Marie-Cornelie Falcon, for whom this French soprano category was named, appears to have been either a dramatic soprano with mezzo-like characteristics (possibly comparable to Jessye Norman?) and a "short top", or a high dramatic mezzo (comparable to Giulietta Simionato).
Chimène in Massenet's LE CID
Valentine in Meyerbeer's LES HUGUENOTS
Rachel in Halévy's LA JUIVE
Sélika in Meyerbeer's L'AFRICAINE, Alice in his ROBERT LE DIABLE, and Catherine of Aragon in Saint-Saëns's HENRI VIII are also Falcon roles, but who the heck does these operas nowadays?
Some other roles to look into:
Eboli in Verdi's DON CARLO
Lady Macbeth in Verdi's MACBETH
Giulietta in Offenbach's LES CONTES D'HOFFMANN (in productions where Hoffmann's three loves are assigned to different sopranos)
Cassandre in Berlioz's LES TROYENS Part I (sometimes the same singer also plays Didon, the more solidly mezzo role, in Part II)
Marguerite in Berlioz's LA DAMNATION DE FAUST (before anyone insists this is a lyric part because Von Stade and Graham have sung it, I shall remind you of the brilliant assumption of the part by dramatic soprano Regine Crespin. If Charlotte in WERTHER can be sung by a dramatic, Marguerite in DAMNATION surely can.)
Donna Elvira in Mozart's DON GIOVANNI (if you've got the agilità)
Elettra in Mozart's IDOMENEO (again, if you've got the agilità)
Komponist in Strauss's ARIADNE AUF NAXOS
Joan of Arc in Tchaikovsky's ORLEANSKAYA DEVA
Leonore in Beethoven's FIDELIO (Christa Ludwig being one of the best ever)
Eventually, if you've got a thirst for singing Wagner, you may want to investigate Venus in TANNHAEUSER, Ortrud in LOHENGRIN, and Fricka in DIE WALKUERE. Further down the road, you may grow into Kundry in PARSIFAL, Sieglinde in DIE WALKUERE, and the GOETTERDAEMERUNG Bruennhilde.