In a team that only sells in euros, a currency field seems unnecessary. The problem starts with the first customer abroad: a quote in Swiss francs or pounds is entered as a plain number, and from that moment the pipeline total, the forecast and the win figures mix two currencies without saying so. Pomio CRM recommends recording the currency on every deal, so the amount always means what it says.
The currency is part of the amount
An amount without a currency is incomplete in the same way that an amount without a VAT agreement is: deal amounts are best entered excluding VAT, and they are only comparable when everyone knows the currency as well. That matters as soon as every open deal has an amount and those amounts are added up per stage or per month.
A fixed list with a sensible default
Use a short list of the currencies you actually quote in, such as EUR, CHF, GBP and PLN, written as the standard three-letter codes, and set your home currency as the default. That way nobody has to choose for an ordinary domestic deal, and a foreign deal is a conscious choice. Free text quickly produces “€”, “EUR”, “euro” and “Euro” side by side, which breaks every filter, just as with labels that are not a fixed list.
Keep the quoted amount, convert in reports
Store the amount in the currency the customer was quoted in, because that is the figure on the quote and the contract. Converting it on entry hides the real agreement and makes the deal wrong as soon as the exchange rate moves. For pipeline and forecast totals, convert to one reporting currency in the report itself and state which rate and date you used. Then the monthly comparison of forecast and actual results shows real sales differences instead of exchange-rate differences.
Agree who may change it
Changing the currency of a deal changes its value as much as changing the amount does. Treat it the same way: once a quote has been sent, change the currency only together with a short note, as with a changed deal amount. If recurring and one-off revenue are tracked separately, both parts of the deal use the same currency, so that the split between recurring and one-off revenue stays comparable.