I'm unaware of any magic item that grants disadvantage to enemies attacking allies other than you.
One might exist but i've never seen it come up. I would therefore assume that one does not exist in the extant rules. If one exists, it very likely requires that you attack the enemy in question, as nearly all extant class abilities (and feat) that do something similar require an attack (and one that hits, in most cases).
You probably want the Sentinel feat.
While it does require you to attack the target you are stopping from moving, other enemies will not be then able to 'gang up' on you to remove the obstruction without suffering from half damage. If you choose the strongest melee enemy in the group to use Sentinel on (and to focus your attacks on), while you won't halve any incoming damage from that enemy, the halving of other enemy attacks will force them to choose between spreading their damage around (most dangerous one on you, the rest on the rest of the party), which is bad, or attacking someone who halves incoming damage, which is bad.
You will still be a worse tank than a barbarian or a fighter.
A barbarian halves incoming damage from all enemies regardless of who they've hit, especially if a bear totem barbarian. A Cavalier fighter can lock down a very high number of enemies with their level 18 feature, Vigilant Defender, in combination with their level 10 feature, Hold the Line (basically the Sentinel feat), and their level 3 feature Unwavering Mark.
Paladin has other benefits, such as Lay on Hands and Aura of Protection (the big one). But in terms of intercepting enemy attacks and surviving under incoming fire for the longest, Cavalier fighters lock down dozens of enemies and barbarians hold up the longest. Even Bladesinger wizards can do tricks with high AC and the Shield/Absorb Elements spells to avoid huge numbers of attacks, to a degree that makes them tougher than paladins depending on enemy composition, on top of being able to teleport to safety if in danger and throw down wall of force or forcecage to tank using pure magic.
In other words, nothing wrong with playing a redemption paladin, but if you're choosing it for mechanical reasons there are better options - from a fighter cavalier with a lance he uses to keep people at 10' distance, to a Crown paladin who aoe mind controls people into fighting her, to just a barbarian who has huge trouble actually dying.