A Bag of Holding modified by a wizard.

Inside the bag are several pocket dimensions:
(1) a library filled with books, a desk to work on notes and spell copying/crafting, and non-plant-based material components used for spellcasting neatly arranged and labeled. There is also a cozy sitting area for reading and relaxing, with an arcane light globe simulating different stages of natural light nearby.
(2) a workroom that can be modified upon attunement to provide whatever workspace that wizard in particular would find most useful (alchemy, fabrication, enchanting, etc)
(3) a magical garden already planted and lush with many things commonly needed for plant-based material components
(4) - (6) are pocket dimensions that can be totally crafted and created by the wizard upon attunement; once the item has been attuned over a long rest, the wizard can imprint their desires upon the remaining rooms much like with Magnificent Mansion and Mighty Fortress and specify what those rooms will look like.

A creature can survive and breathe in these pocket dimensions and can enter and exit through the opening of the bag.

Placing a bag of holding inside an extradimensional space created by a handy haversack, portable hole, or similar item instantly destroys both items and opens a gate to the Astral Plane. The gate originates where the one item was placed inside the other. Any creature within 10 feet of the gate is sucked through it to a random location on the Astral Plane. The gate then closes. The gate is one-way only and can't be reopened.

Notes: Wizard, Utility, Container