Double knitting is also called 8 ply and Aran is 10ply. Two test squares would be the best to see what works size wise. 4.5cm knitting needles would work best I think. Can you compare the length of the suggested double knitting wool to the length per ball of the Aran and see what the difference is and work out how much yarn and therefore how many balls. It may work out that the number of stitches for a 44Dk will be very similar to the number needed for a 48 Aran.
Best of luck.
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