SERIAL for multi-column unique constraints

I'm trying to build an append-only data model in Postgres, using the following schema:

CREATE TABLE IF NOT EXISTS account (
    id UUID DEFAULT uuid_generate_v4(),
    user_id INT NOT NULL,
    currency_id INT NOT NULL,
    balance INT NOT NULL,
    version INT NOT NULL DEFAULT 1,
    PRIMARY KEY(user_id, currency_id, version)
);

The idea is to have n users, owning m accounts. Each account is connected to a certain type of currency and can have a balance. Changes to the balance are persisted by adding a new row to the table (as opposed to updating the current row) and increasing the version field by 1. The latest balance of a user would always be found by SELECT balance FROM account WHERE user_id=? ORDER BY version DESC with a full history of balance changes. I should be able to solve this using multiple queries in a transaction (if exists, read version, then insert new row with version+1). But I was wondering if there was a more clever way of designing the table structure itself (something like a SERIAL that would only increment on inserts in the same unique constraints). I assume it probably won't be as straight forward as this, but I thought I'd ask.