If you're looking for works that echo the raw, fragmented introspection of 'Not I', Samuel Beckett's other plays like 'Krapp’s Last Tape' or 'Happy Days' dive deep into existential isolation with that same razor-sharp minimalism. Both strip human experience down to its core, though 'Krapp' uses a tape recorder as a haunting device for memory, while 'Happy Days' buries its protagonist literally in sand—visually poetic and just as unsettling.
For something more contemporary, Sarah Kane’s '4.48 Psychosis' hits with a similar emotional sledgehammer. It’s chaotic, lyrical, and blurs the line between monologue and free verse. Thematically, it grapples with mental disintegration in a way that feels like a companion piece to Beckett’s disembodied voices. If you enjoyed the disembodied mouth in 'Not I', Kane’s work might resonate—it’s like staring into an abyss with no comforting edges.