Hi yes i use Abbey too for my stirrup butts they are nice but there are alternatives, although one maybe more expensive - had a price list for them from about a year ago not sure where it is or if it is up to date, email them for a quote, never used leather from but never heard a bad word about them other than its not cheap J&JK Baker.
The other is Metropolitan leather, which i use a lot, near enough for me to drive and select the leather i want - they do two weights of bridle butt the heavy one is 5mm which possibly could be used for stirrup leathers, again email them and asked their opinion on this. I do know on one old review on the 5mm, the saddler had said it was ideal for stirrup leathers this maybe a cheaper option. I have used both weights in various colours and have been happy with it makes lovely bridles.
As for laminated stirrup leathers, yes have used them when working in horse racing, the quality varies - some have been ok but they can become very scruffy if not maintained and looked after the stitching on the laminate can wear and look very unsightly, not to mention safety - although the better quality ones do seem ok.
http://www.jfjbaker.co.uk/equestrian-leather/stirrup-butt/
https://www.metropolitanleather.com/Buy-Leather/Buy-Vegetable-Tanned-Leather/Coloured/Coloured-Old-English-Bridle-Butt
Hope this helps
JCUK