I’d say Ferrothorn. With decent attack and great 74/131/116 defenses, it is an excellent wall. It has access to Curse, Thunder Wave, Spikes, and Stealth Rock as far as boosting/supporting moves go. For offensive moves it gets STAB Gyro Ball, Bullet Seed, Seed Bomb, and Power Whip. Like I said, it also has good attack, at base 94. Flygon covers up its Fire weakness, and it covers Glaceon’s Rock weakness. It’s only problem is that it has a 4x weakness to Fire and a weakness to fighting, both of which Glaceon have as weaknesses as well.
Another good wall is Umbreon. With great 95/110/130 base defensive stats, it makes an outstanding wall. The only problems with Umbreon are that it unfortunately lost Toxic this gen, and it relies on Foul Play for attacking, as its attack stats are trash. It is faster than Ferrothorn, but Ferrothorn gets Gyro Ball to make its low speed an advantage. In gen 8, it gets Confuse Ray, Taunt, Moonlight, and Wish for stalling moves. And, as far as attacking goes, it can really only pull off Foul Play, though Snarl makes it more specially bulky and Dark Pulse... it’s ok.
Note that Umbreon can get Toxic if you trade it from another game, but directly from SWSH, you can’t get Toxic on an Umbreon.
Hope this helps! :)
By the way, I’ll try to add more Pokémon to this list, I’ve just gotta think of more walls :P