I am planning on using a bareback pad with sturrips
Seriously just don't. Not only does that put ALL your weight on a very narrow strip [which is a lot of pounds per square inch even if you're a really light person], most people also rely on their stirrups for balance, which is a really stupid idea in a bareback pad because if you put more weight in one stirrup than the other the pad WILL slip and you WILL fall off. Probably get dragged, too.
I have seen far more nasty nasty accidents as the result of a bareback pad with stirrups than I have seen in any other circumstance. I haven't HAD any such accidents because I refuse to use such dangerous equipment. Bareback pads WITHOUT stirrups are a-ok, but with them they are a recipe for disaster.
Regarding the OP... a driving pony will generally make a reasonable riding pony. A good driving pony has to be quiet, because driving is more dangerous than riding when things go wrong. It also has to be good in the mouth, and will have been desensitised to things on its back already. They're not difficult to break to ride if they've done well in harness, mainly because they've had a huge amount of the foundation work already done to get them ready for a rider. HOWEVER, even so, you really don't want to be breaking a pony to ride all by yourself. Get help. It's much easier with help. The more experienced and qualified that help, the better - and in BREAKING, not just riding!
When I start to ride, I start them first as if I were intending to break them to harness. Roller on, straps hanging off here there and everywhere, make sure they understand giving to the bit vertically and laterally as well as reinback and halt... then long lines on and ground driving. Once they are proficient at that, then and ONLY then do I put a saddle on... and let them get the buck out without a rider. For the initial stages of breaking the saddle doesn't have to fit because nobody will be sitting in it; so long as it's reasonably close it's ok. Once the horse is ready to take weight on its back for the first time, however, it is IMPERATIVE that the saddle fits, because the last thing you want is for your pony to associate a rider with pain.
Best to break in a saddle because it does give you that little extra grip. It concerns me greatly that you have a pony and can't afford a saddle for it, to be honest... my breaker saddle has a market value of MAYBE $30, cheap second hand rather worn out old thing that it is. You can get a lovely high quality second hand leather saddle for under $500 if you shop around. If you haven't got $500 for a saddle, what are you going to do for vet fees if your pony gets sick or injures itself?
Very important that your pony doesn't learn it can buck you off. Once is enough to create an evasion which even an experienced rider might struggle to fix. The horses I've had a hand in starting don't get opportunities to buck, and I know I can ride a good one.
First thing I always do is the saddle because if I can get that on and girthed, I can get some buck out of my horse before I get on. Then I put a little bit of weight in the saddle with my hands, and very gradually work my way up to sitting on their back briefly. I mount and dismount until I'm getting vertigo from the constant changes in altitude, then mount and dismount some more until my horse is utterly bored with the whole caper. Then I stay on a while and get someone to lead the horse at a walk. From there I teach leg aids, and because the horse is already mouthed before I get on its back I don't have anything to teach regarding my reins. Once my horse has well-established leg aids, my helper gets a break while I establish confidence with no person at the horse's head. Once that is well-established it's back to the helper for the trot, and once everything is established there, I will typically ride trails with company and on a nice straight even-footed stretch, get my helper to ask their horse to canter, and allow my mount to just fall into it. Once that's ok I start introducing aids and correct leads, and once that's all established my horse is green broke.
First canter it's best to be prepared for a bit of bucking but if they are prepared properly not many horses buck. It's all about preparing them right, though, and that takes a lot of feel, timing and patience.
I am not 100% on how to get a horse from green broke to "broke with basic education" but hey, I'm not at the stage where I need that knowledge yet. Not with my filly, not with Mum's filly.
Do bear in mind that I've only "half broke" 3 horses, two are too young yet to get to the stage of being green broke and one was sold from under me when I was a little kid. My opinion comes from a LOT of reading up, a LOT of theory knowledge, but very little practical knowledge.