The way round that is to set your phone to either warn you or cut you off if approaching the limit, then you know when to buy the boost.
Android can do both. But its not immediately obvious, have to go into wifi and internet settings, then data usage, then mobile data usage, then tap billing cycle, then you should finally see the settings you can adjust the monthly limits, also the billing date can be adjusted there.
I sent EE a query about them sending me proof my terms of sale showed clearly I would be liable for inflation busting annual rises (to try and get them to let me leave penalty free 7 weeks early), then 20 mins later retentions called me and beat the 1p mobile pricing whilst also exempting me from 2023 rises (12 month deal so will be in driving seat again in 2024), so for a year now I will be staying on EE, but I had full intention of moving and wasnt expecting them to give such a big discount. 1p mobile I think is a cracking deal assuming the boosts can be ordered without a sim swap.