Create a single filter to filter across two columns

Hi,

I'm terribly sorry if this has been asked multiple times however I can't seem to find a quick solution to this query.

I have a dataset that has multiple columns, two of these columns are number columns with numbers between 1-12 for months (whole number). My data might look something like this:

Col1   Col2   Col3  Col4

fywh    12      3        £100

hujq     10     5         £501

I need to create a line graph with col2 & col3 as the bottom axis, col1 as the y axis and col4 as the value. Easy enough however I need to be able to toggle between Col2 & Col3 to reflect the cost at the different months.

How I've done this is to add a custom column to merge Col2 & Col3 with an identifying in between. Such as: 12, Col2; 3, Col3

After much Power Query magic I basically managed to duplicate all lines of my table so it now looks like this:

(I followed steps as per this page to action this: https://community.powerbi.com/t5/Desktop/How-do-I-duplicate-rows-based-on-cell-contents-cell-contains/m-p/200671 )

Col1   Col2    Col4    Col5

fywh    12      £100    Col2

fywh    3        £100    Col3

hujq     10     £501     Col2

hujq     5       £501     Col3

This is great because it allows me to create the line graph that I want and set a filter for Col5 to filter the dataset...in theory and small practice yes...

The problem I have is that in reality my dataset is over 2 million lines (and counting) so to action this each refresh the report just can't copy. 

There must be a simpler way of actioning this. I was thinking of a filter table with the identifyers in then a DAX measure to filter across Col2 and Col3 that way. Would this be the best thinking? I have tried a relationship but I can't see how this would work as there isn't any way of connecting to the main data (I would have to create the identifyer column to do this)

I'm sorry if this doesn't make sense! 

E