What to look for in a good waterproof jacket

What sort of activities are you using it for? Hiking, watching the kids play football, work? Are you working hard while it is on?
When you say the breathability is poor, what's happening? Is it wetting from outside or inside?

In general, the more layers you have the more flexibility, so you're doing the right thing there by keeping it light.

From experience I've found that if you want a jacket which will last hours in the Irish rain when hiking, and is breathable, you're talking a stiff and heavy jacket which costs big bucks. And these jackets are too heavy for Summer use I find. Pit-zips are handy in heavier jackets to release air.

What I've found myself increasingly doing is packing two lighter rain jackets on bad days, and swapping them over if one wets out. I'm not crossing South Georgia, I don't need bomb-proof gear. Most of the time I'll just carry a single lighter jacket unless persistent rain is forecast.

Gore-anything is good because you know what you are getting. Most of the specialist hiking brands will have good gear and often use their own technology (e.g. Pertex), but the more you pay usually the better the quality. Good brands would include companies like Montane, Rab, Berghaus, Salomon, Mammut. There are a couple of websites where you can find discounted hiking gear from good companies. I personally prefer to buy good gear when it is on sale, rather than cheap gear at any price