Currency sinks alone won't save you, even if you're not creating free money from resources. If your number of players changes, then the distribution of money will change also. And if you scale the money supply linearly to match the number of players, that does nothing for the inequality of wealth distribution (which will tend to get worse as the numbers rise) and it tends to ignore that your new players don't have an 'average' amount of money but in fact start off in relative poverty. It's incredibly hard to get right which is why the real world doesn't do a great job of it either, despite having a more closed economy.

In my view the best thing to prevent inflation is to avoid currency altogether. If your game design allows for a barter-based system, that can help, because it's typically harder for players to manipulate the flow of goods. (Someone who can carry 10,000 gold pieces can rarely carry 10,000 pigs worth 1 gold piece each.) A compromise is multiple currencies with unfavourable exchange rates, which coerce players into preferring goods over stashes of cash.