At least that narrows it down to the last year or so of the war - the best documented which is both a blessing and a curse.
As you know Larpent is the best source for Headquarters for that period. Wellington's Voice - the letters of John Fremantle might also be good and also the Napoleonic War Journal of Thomas Henry Browne.
But I've not seen anyone give much detail about the stables and the horses - or maybe I just haven't noticed it.
Anyway good luck with your research.