South-facing windows are definitely a good start, but most lemon trees really do thrive with a bit of extra help, especially in winter. I’ve found that a full-spectrum grow light made a big difference for mine-more consistent growth, no leggy stems, and actual fruit! If space allows, a small oscillating fan also helps with airflow and keeps pests down. Curious what variety you’re thinking of growing? Meyer lemon trees tend to be the most forgiving indoors.