Replacing offset with non-volatile functions

I'm looking to replace offset with non-volatile functions. I use it in sumif formulas to find the column or row to sum, for example,

=sumif(A:A,"yes",offset(A:A,0,match(1:1,"December",0)-1))

Index works okay if I am looking for a row, but what can I use if I am looking for a column like the above formula?

Thanks

Attach a sample workbook. Make sure there is just enough data to demonstrate your need. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are shown, mock them up manually if necessary.

Remember to desensitize the data.

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Great, that's perfect, thanks very much