In the 10.5, I don't think my foot slides around too much... really, my left foot feels great, but the big toe of my right foot is not so happy, especially when standing straight up or going on heel.
Will the footbeds / insoles increase the amount of space for my toes up front?
I saw in some of the pictures it looks like the footbeds would elevate the back part of my heel. Which products do you recommend?
If your toe is digging into the 10.5 I'd personally go with the 11. If it fits a little spacy then you can add shims to fill the space. And as the boot leather softens up you'll be able to pull the laces tighter around the foot.
I use Superfeet insoles and Tognar fitting foam. I have relatively thin feet so I use a piece of foam over toe on top the the liner. And if the liner packs out I'll use a piece of foam behind the heel like this
This way the boot fits compact without jamming up all day.