For your tables, Iโm curious if you could utilize Liquid Clustering to reduce some of the maintenance issues relating to choosing Z-Order vs. partitioning.
Saying this, one potential way is to read the Delta transaction log and read the Add Info statistics which includes the file path and size.
You can query the transaction log add info directly to extract out all the files that are associated with a particular month to calculate its size.
You can also find more info about this at A peek into the Delta Lake Transaction Log.
HTH!