https://drop.com/audiophile/drops
Mass drop is a fantastic place to buy headphones. There can be a bit of a wait, you are essentially trading big savings for waiting for them to ship in batches.
I have the sennheiser/drop 6xx. They sound pretty fantastic to me and a phone is enough to drive them directly. They are open back so they don't have much isolation however. If you are listening in a public or noisy place, go closed back.