If you have space between your toes and the boot toe box when you try them on, your problem is not length of the boot. The problem is your foot is sliding forward with gravity on descent. A longer boot is not going to stop that from happening, more length will give your feet more room to slide forward. You may also give up the advantage of having physical awareness of your boot support/foot positioning when using toe-holds on ASCENTs as well.
A trick skaters have used for a very long time is to lace yourself in so your foot cannot slide forward. That protection happens over the instep, the top side of the arch of your foot. Being secure at the instep prevents sliding forward, and also prevents heel slippage that causes blisters from rubbing against the boot heel.
Try a half hitch or two in your boot laces at the point over your highest arch, often times where the lacing turns from " holes" to " speed hooks".
If the boot is too stiff to lace down snugly over your arch, ( and you may WANT that stiffness in the boot for other reasons), as others have said, use a footbed, full or partial, to raise your foot higher in the boot, or use a little padding under the tongue of the boot when you lace up. It's about securing your foot so it DOESN'T slide forward.
Skiers have the same issues. Feet are not mass produced, and many people find when it comes to high- performance footwear, that even their own 2 feet are not the same.