My tall boots from Sergio Grasso are the most comfortable I've ever walked/ridden/ran after loose horses/trekked through the mud/cleaned stalls/gone to lunch in! They come in every variety of size imaginable AND are FEI approved. I wear mine every single day. You will not be sorry that you bought these boots. 
 
These lovely boots feature the following: 
Nappa calfskin upper and lining
SG Ultratech calf panel ensures perfect grip in the saddle
Rear reinforced elastic
Front fastening with elastic laces
Rear zip
Zip protection and spur rest
Spanish cut
Walk&Ride technology