Yes , I agree , I take a 10 in shoes but 11 or even 11.5 in Walking boots,
you can always put an extra pair of socks on if they are a bit loose and I find feet do tend to swell slightly on a long walk.
Have found Boots insoles effective when suffering from plantar faciitis
(hope I've spelt this right)They cover the heel and instep only .Cost about £20 .