Get a barghest to eat you1
This is probably the easiest solution, since barghest will attempt to consume goblinoid leaders. Simply pose as one using a spell like alter self and you can easily attract the attention of a barghest.
The section on the barghest in Volo's Guide to Monsters (p. 123) states
A barghest can feed on the corpse of a humanoid that it killed that has been dead for less than 10 minutes, devouring both flesh and soul in doing so...
Once a creature’s soul is digested,... no mortal magic can return that humanoid to life.
1: credit to guildsbounty for the mention in the comments
Ask a lich if (s)he'll consume your soul for you
The section on the lich in the Monster Manual (p. 203) states:
Soul Sacrifices. A lich must periodically feed souls to its phylactery to sustain the magic preserving its body and consciousness. It does this using the imprisonment spell. Instead of choosing one of the normal options of the spell, the lich uses the spell to magically trap the target’s body and soul inside its phylactery. [...] A creature imprisoned in the phylactery for 24 hours is consumed and destroyed utterly, whereupon nothing short of divine intervention can restore it to life.
While Divine Intervention could still save you, I'm not sure you'll find an option that circumvents Divine Intervention other than Divine Intervention itself or wish (both below).
The typical options
The 9th level wish spell can do almost anything with GM permission:
You might be able to achieve something beyond the scope of the above examples. State your wish to the DM as precisely as possible. The DM has great latitude in ruling what occurs in such an instance, the greater the wish, the greater the likelihood that something goes wrong.
The cleric's Divine Intervention feature might work as well:
Imploring your deity's aid requires you to use your action. Describe the assistance you seek, and roll percentile dice. If you roll a number equal to or lower than your cleric level, your deity intervenes. The DM chooses the nature of the intervention