On top of all the options mentioned above, there are two more that I can think of, though neither are permanent.
The first is the item Eldritch Claw Tattoo from Tasha’s Cauldron of Everything which requires attunement. It has an ability called Eldritch Maul which change your base reach to 15 feet instead of 5 feet.
Eldritch Maul. As a bonus action, you can empower the tattoo for 1 minute. For the duration, each of your melee attacks with a weapon or an unarmed strike can reach a target up to 15 feet away from you, as inky tendrils launch toward the target. In addition, your melee attacks deal an extra 1d6 force damage on a hit. Once used, this bonus action can't be used again until the next dawn.
This is stackable with any bonus to your reach but it last only 1 minute. That being said, it is enough to cover most combat situation, but it requires you to have access to this item.
The second one is a Dark Gift from Van Richten’s Guide to Ravenloft. Being setting specific, it may be accepted or refused in other settings, you would have to check with your DM. You would also have to check if Dark Gifts are accepted at your table.
This Dark Gift is called Living Shadow it has the feature Shadow Strike which gives a number of attacks a +10 to your reach.
Shadow Strike. When you make a melee attack roll, you can increase your reach for that attack by 10 feet. Your shadow stretches and delivers the attack as if it were you. You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
This feature can be used only 2 to 6 times per long rest, though.
Meaning that if you have them both and activate them too, you could have:
Base: 15 ft. (Eldritch Maul)
Bugbear: +5 ft.
Lunging Strike: +5 ft. (Battle Master)
Fangs of the Fire Snake: +10 ft. (Monk)
Potion of Giant Size: +5 ft.*
Shadow Stike: +10 ft.
Avernus’ Demon Ichor: +5 ft.
(see the specifics for most of those in posts above)
Which gives a total of a 55 feet reach.
*The miscibility optional rule for potions (see comment above) has also the possibility to double its effect which would bring it to a grand total of 60 feet. Though this is completely unpredictable and based on an optional rule that your DM may not use.