I know that custom made footbeds are highly recommended, but I would appreciate your opinions on what other options are significantly better and worth buying (if any) than the stock insole that comes with a new boot.
The average, healthy foot has several arches which need to be supported in order to spread load and improve control---it is important to support the medial arch from heel to ball of foot, something that seldom happens in an over the counter insole. There is also an arch on the pinky toe side of the foot that is never supported in an over the counter insole, at least I haven't seen one that did. In most feet there is also a metatarsal arch going across the forefoot at the met heads, also not supported.
The over the counter footbeds are better than most factory insoles as they (factory) are usually just a pad, and no support at all, most over the counter footbeds will have a deeper heel cup, which will center the foot/heel in the shell better.