Great! It sounds like you’ve made a good start with intervals and triads, so I would recommend:
1. Firm up this foundation. Keep practising major and minor triad chords. Keep working on your interval recognition.
Resources:
2. Start working on seventh chords. Introduce one type at a time. Start by practising with the dominant seventh vs. major triad chords. Then introduce minor sevenths and major sevenths. Use your triad and interval recognition skills (particularly major 7ths vs minor 7ths) to help you pick apart the chords by ear.
Resources:
Does that help?