Virtual cards
Spend the dollars
you already hold.
Your balance stops being something you look at and becomes something you spend. Issue a virtual card against your USD or GBP account and your cloud bill, your ad spend and your suppliers are charged in a currency you already own, at a limit you set, on a card you can freeze the moment something looks wrong.
Spend the balance, not a conversion
A card draws from one currency account, so your dollar subscriptions are charged against dollars you already hold. The conversion you were paying on every renewal simply stops happening.
One card per line item
Name it, colour it, cap it. Give the cloud bill its own card and the ad account another, each with a per-transaction and a daily limit, so a runaway charge stops at a number you chose.
Disposable cards for one-off spend
A trial you do not want renewing, or a supplier you will use once. A disposable card blocks itself the moment its first charge succeeds, so it cannot quietly be billed again.
Freeze now, decide later
Freeze a card the second something looks wrong and unfreeze it when it does not. Frozen is not closed, and the full number is shown once to the person who needs it, then never stored.