I'm going to flag this again because I think the links I posted could be useful.
Last week, over on my Army Ancestry Research blog, I published a list of infantry and foot guards regiments with links to those regiments' surviving service and pension records on Findmypast. I was quite surprised at how many records survive for some regiments and how few survive for others.
The records cover a wide year range, from 1760 to 1920, although the majority will be for the period 1881 to 1918. Clicking on the British Army infantry and foot guards links I published will take you to the search results but you will need a subscription or pay-per-view credits to actually view the records. You'll also find some of these on Ancestry but Findmypast has a far more comprehensive and better indexed collection.