For anyone who is interested, CoquiTTS (formerly, MozillaTTS) was great, but the project isn't maintained anymore (athough there's been some confusion about whether or not it's active. See: https://github.com/coqui-ai/TTS/issues/4022).

Looks like there's an effort to keep an actively maintained fork here, though: https://github.com/idiap/coqui-ai-TTS