It’s not a prepaid card you specifically need - it’s the local payment network and essentially all credit/debit cards issued locally support NETS.
What’s this talk about MRT being cashless? Does it mean cash is no longer accepted to top up ezLink/Nets Flash Pay cards at stations?
Some stations no longer accept cash for top ups, you can still use machines and pay by other means. Cash topups remain readily available in convenience stores.
See here for all of the top up locations. 7-11stores seem like the easiest. Keep in mind the ATM topup can’t be done with Monzo cards.