My answer will be based on Spells. I can't remember any magic item that works like what you want (except for casting these spells).
Contingency from a Wizard multi-classed into a class that can cast resurrection spells, e.g. Wiz 11/Cleric 9. Not optimal, but official. Note that Contingency only states
spell that you can cast
not "A Wizard spell".
If you have access to a Contingency spell scroll, you can read it if you have at least 1 level in Wizard. Note that you can only cast a spell from a scroll
...if the spell is on your class's spell list, you can use [it]...
The use is simple: Trigger is "me dying", spell is Revivify. Other res spells have cast time of 1 hour, not 1 action (Raise Dead, Reincarnate, Resurrection and True Resurrection at least - can't remember any other).
The first time the target would drop to 0 hit points as a result of taking damage, the target instead drops to 1 hit point, and the spell ends. If the spell is still in effect when the target is subjected to an effect that would kill it instantaneously without dealing damage, that effect is instead negated against the target, and the spells ends.
Not exactly being resurrected but stopping death, which is essentially the same.
Well, Wish can do anything as long as you word it correctly and your DM allows it. "I wish that next time I die, I get instantly resurrected". (Or resurrected after 1 week, or anything else you... Wish.)
Anything that grants you a cast of any of the earlier spells
Welp, obvious one as well. In particular, Gate into Efreeti into Wish. Candle of Invocation works as well, but your DM will not be giving one to you.
Depending on your definition of "others"...
You could also have creatures conjured (or enslaved?) for you that can cast resurrection for you. True Polymorph gives you a friendly creature (from a rock). PixelMaster has mentioned War Priest, from Volo's Guide to Monsters, who is CR9 and can cast Revivify - there you go. Find a large rock, cast True Polymorph, create a War Priest.
Glyph of Warding - slightly modified
Since this errata, Glyph of Warding can also be used for that purpose.
Originally it said
When you cast this spell, you inscribe a glyph that harms other creatures
but it has changed to "When you cast this spell, you inscribe a glyph that later unleashes a magical effect."
Spell Glyph: You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph. The spell must target a single creature or an area. The spell being stored has no immediate effect when cast in this way. When the glyph is triggered, the stored spell is cast. If the spell has a target, it Targets the creature that triggered the glyph. If the spell affects an area, the area is centered on that creature. If the spell summons hostile creatures or creates harmful Objects or traps, they appear as close as possible to the intruder and Attack it. If the spell requires Concentration, it lasts until the end of its full Duration.
You decide what triggers the glyph when you cast the spell.
As per V2Blast's comment, if you define the trigger as being "It triggers when I die", you are the one triggering the effect, thus you're the target. You could then cast Revivify and put the Glyph somewhere.
It's not a Homunculus/free resurrection due to this limitation (clarified in the same errata):
If the surface or object is moved more than 10 feet from where you cast this spell, the glyph is broken, and the spell ends without being triggered
So you can't just cast it in an object and walk with your free resurrection inside the dungeon.
This would be best used in your own house or something like that for not being assassinated.
I've had an (evil tyrant and paranoid) NPC doing that, glyphing his own bed. Just in case someone would kill him during his sleep. It's essentially a (greatly) nerfed Contingency that can be used by other (than Wizard) classes.