Currency system options I'm gonna narrow things down to.
Option 1: Silver Standard coinage.
The Silver Coin is the basis of value making it 1.
The Brass Coin is worth 1/10th of a Silver Coin.
The Tin Coin is worth 1/100th of a Silver Coin.
Orichalcum Coins are worth 10 Silver Coins
Gold coins are worth 50 Silver Coins.
Option 2: Gemstones.
The Bloodstone is a small and cloudy red semiprecious gemstone, often shot with black, and is the basis of economics and is found in four measures of weight and size. Abbreviated as B. For example 100B would be 100 Bloodstones of value.
The Bead: A small and round bloodstone in the shape of a bead. Worth 1B
The Nail: A round bloodstone roughly the size of a fingernail. Worth 10B
The Finger: An oblong bloodstone roughly the size of a ring finger. Worth 100B
Beads weigh .45 grams, and are 1,000 to the pound.
Nails weigh 4.5 grams, and are 100 to the pound.
Fingers weigh 45 grams and are 10 to the pound.
Option 3: Weight Tokens Gold Standard (Could also use Silver, Salt, or other Commodities as a basis)
The Tally is worth 360v. It is a token valued at 30 pounds of Gold.
The Mina is worth 60v. It is a token valued at 5 pound of Gold.
The Deben is worth 12v. It is a token valued at 1 pound of Gold.
The Bead is worth 1v. It is a token valued at 1 ounce of Gold.
Option 1 is the most familiar to D&D players. It uses metric increases and decreases, so it's super easy to handle. We also know Silver Coins as 1/50th of a pound, so that makes weight management super easy. It's a little drab, but it's nothing terrible. It also has -plenty- of room for manipulating both the coins (Shaving, cutting them with other metals, modifying scales) to manipulate it's value.
Option 2 keeps the scale and essentially gives you a heavier Gold Piece standard using Gemstones in a metric fashion. However it has a certain "Humanistic Element" in both the scale of the individual gemstones (A hand would be 5 fingers, for example) but also in measures (10 fingers to the pound).
Option 3 steps aside from our standard understanding of currency by breaking into a Base 12 system, which the ancient world largely used. Easily divided into a wider variety of whole divisors than 10, it also had a humanistic counting method based on knuckles rather than fingers using the thumb of the same hand. Like so:
My current thought is to have the Tally, Mina, Deben, and Bead each carved from different burnished woods rather than metal. Though stone would be an option as well. This would have the side-benefit of allowing money to wear away or even rot over time.
And, of course, these systems could be combined to different degrees. A given society could issue metal Deben, or Gemstone Deben, for example.