1. Do you need to keep your number?
2. Do you need 5G?
3. Which part of Singapore will you mainly use your line?
4. Which Telco (M1 from your reply) is your current Telco?
5. Is your Telco coverage Decent for your current usage?
6. Are you comfortable using MVNO ?
7. How much talktime and sms do you need?
8. How much data do you need?
9. Any price limit you're willing to pay?
Cheapest $5 from TPG senior.
Next is $7 from Zero1.
And Vivifi to MyRepublic....
https://blog.seedly.sg/best-sim-only-mobile-plans-in-singapore-with-singtel-gomo-vs-circles-life/
Simple plans are "unlimited" data plans.
No bill shock. (Eg. Zero1, MyRepublic)
Ultra big data plans 80GB++ (TPG, Etc)
But always need factor in M1/SH/ST have to pay Caller-ID.