Sugar for Marmalade

Hi Lindsey,
I made Delia’s Seville orange marmalade for the first time last year, it was superb! I’ve got my Seville oranges for this year’s batch, but can’t get preserving sugar anywhere! My husband got some 1:1 jam sugar, but I have no idea if this will work: it’s half the quantity of sugar stated in Delia’s recipe and I think it has pectin added already. I’ve heard I can freeze the oranges (until I can get my hands on some preserving sugar) or should I go ahead with the jam sugar? Will this alter the quantity I produce? Any advice gratefully received. Many thanks.