Heel lifts are a ski boot fix. Snowboard boots are not as exact so fixes like that are overkill. Get them molded again with toe caps.
Take out the insole and stand on it making sure your heel is in the pocket of the insole. Does your foot fill out the insole? Or spill over? A lot of spill over means too small.
Second, take that insole you just took out of the boot, and ceremoniously light it on fire and throw it away. It is useless. Go buy some supportive aftermarket insoles. Superfeet and Remind are two good options.