wow thanks guys.
I had a look around and found this.
Moligh doll DDR3L 8GB Memory 1600MHz 1.35V Sodimm 204PIN Laptop for Ddr3 Motherboard https://www.amazon.co.uk/dp/B089KC2WFP/ref=cm_sw_r_em_apa_i_YPS1Eb3844PK3
would this be suitable? does the brand change anything? and does ram deteriorate like a hard drive? ie could I just buy a second hand on ebay and be fine ? seems like it's identical to the ones at 3x the price? thanks.