Adjusting the custard for trifle

I'd like to make Delia's traditional English trifle and, due to allergies, would have to replace the cream with A2 cream. Unfortunately, A2 cream is not available here so my only option is A2 3.25% homogenized milk. Could you please advise me what changes (extra egg, corn flour, whatever..?) I could make to Delia's recipe to achieve a good consistency of custard for trifle?
Thank you very much.