Hi,
Yes, if your horse is conventionally shod - that is, peripheral rims, he is at just as much risk of stone bruising as if barefoot. Perhaps more, because soles are very often thinner on shod horses, due to a number of factors. So yes, horses do best with protection/support *under* their feet, where necessary. Shoes aren't at all all bad. But they are a compromise on many levels. So to pad/shoe is still going to effect the feet in much the same way. They're also stuck on his feet, 24/7 for quite a few weeks running, leaving his feet more susceptible to infection, and also to overgrowth further compromising function.
Hoof boots on the other hand, while still a compromise in some ways for the horse, don't tend to inhibit hoof function, you can use extra foam pads if/when you feel the need, and they provide protection and support to the whole base of the foot. You only use them when needed - eg when the horse is working; it is quite uncommon for a horse to be so seriously lame as to need protection 24/7 in his paddock... & if so you should be very concerned & not working him either - there's more than just boots he requires! Having the horse barefoot for the majority of the time allows them to be better managed, kept in functional shape, free/treated from infection, etc.
As for what type, virtually any type made for riding in will protect his feet adequately enough. It depends on mileage, on what terrain, as to whether some boots are better than others in certain situations/for certain horses. Some boots - like Epics for eg - are a little hard to get on & off, esp to begin with, when you're getting used to it & also 'breaking the boots in'. While some, like Cavellos, Trails, Renegades, are quite easy to put on & off. There are pros & cons to them all, which you need to consider. Easycare has some great info on choosing appropriate boots for your situation(regardless of whether you choose one of their models), on their site. But no. 1 importance when choosing boots is that they fit the horse well. Some types are made for different hoof confos. Some have more 'leeway' fit-wise than others.
I feel I must elaborate on some of what Walkin has said...
1. See above. Your horse is unlikely to need boots in the paddock, unless he's in a very bad way. In which case I'd absolutely get him out of shoes too.
2. Yes, generally, hooves need to be maintained every 4-6 weeks to continue fitting the boots. Depends, but most horses & most boots still suit eachother up to about 4 weeks. Some more leeway than others. For eg Gloves, with no fastening system, are designed to fit tightly, on virtually undistorted feet, and as such, they do indeed tend to need more than 4-weekly 'touch up' trims. They're more for your owner-trimmer. But Cavellos, Trails, etc, and... I forget the name of a more flexible, conforming model... can generally get by with a fair bit of overgrowth.
Remember, how much/little you might need to trim to fit certain boots, especially when you've got hoof probs - such as thin soles, distortion, etc - it's best for the horse if you trim frequently enough to *maintain* functional form, rather than leave it until the hooves are obviously overgrown before 'correcting' each trim.
Re expense, yeah, that is a factor, esp if you're not sure what's best. But there are sources to buy secondhand boots these days, and some even loan/hire them to try. You could also consult a boot fitter(hopefully also a trimmer, kill 2 birds...) who knows a number of brands, to ensure you're getting what's best, and can generally return/exchange them thru the fitter if they aren't appropriate.