@ab1 Yeah BA9S was perfect - still haven't tried rewiring them yet but i'd say that should work
a month later
I haven't had a go at rewiring the bulb holders I mentioned yet. Something kind of related though, I found in this article on OVT that they had suggested a specific flasher relay suitable for LEDs, and since mine was buggered I figured i'd give it a shot.

The relay was only $15 on eBay and works great, only for standard halogen bulbs so far.
The buggered one (OEM) either did not flash at all, flashed slowly for a short time and stopped all of a sudden, flashed quickly for a longer time and stopped all of a sudden, or stayed on with the switch but did not flash at all.

The new relay has the same terminal labels as the OEM one, and plugs right in. It is about 2/3 the length but the same diameter. If your indicators are giving you strife, then definitely grab one. The flash rate is faster than the slow of the old one and slower than the fast, and the tick noise is about 1/3 of the OEM one.

I'm going to order some indicator, park, brake and reverse LEDs soon based on that guide and give them a go. I'll post the results :)
4 months later
I finally got some 1156 LED bulbs, cheapest ones I could find on eBay. They work really well, very bright. I think I would recommend people buying coloured LEDs where possible, since my lights are OK colour wise, but still could be better. I will probably buy coloured down the track. The indicators and brake lights work great, and toggle on and off very nicely with the relay I have.

I was able to use 1156 bulbs on everything but the reverse bulbs and front park light bulbs. I believe this is because I need 1157 bulbs for these, which i'm going to order. The other thing is the brake light bulb isn't as bright as i'd like with a 1156, so i'm going to try using a 1157 for that too. Once I confirm whether one way is better than the other, i'll post quantities of what I would buy if I were to do it again.
The cheapest ones I notice on the road don't throw the light how you need them and make the lights look small I find. Not the best situation. But you can tell that yourself of course.