Bare Minerals Prep Step is a SPF50 primer, but it's quite runny and thin so it's hard to be sure you're applying enough. The most common advised amount is 1.25 ml for face and same again if you're applying to your neck too. Bare Minerals is expensive to use that amount of daily, and that's not even considering reapplying if out in the sun.
I measured La Roche Posay (non tinted sensitive eyes one) into a children's medicine spoon and it's more than you'd think, and quite hard to rub in. But that particular one is pretty thick and would double as a moisturiser.
Recently bought The Inkey List SPF 30. It's tinted but disappears on my skin (I'm white, quite fair but leaning towards tan/yellow/olive tone rather than pink toned). Not suitable around the eyes though - there's a big warning on it.
If you use SPF 50 you have a better chance of getting pretty decent protection even if you don't apply the correct amount, you might still end up with SPF 20/25ish, whereas with SPF 30 you might down to SPF 10/15, which isn't much at all.
Heliocare is a popular brand I've seen mentioned in skincare groups/boards.
SPF is hard to get right. I've seen people mentioning that their method is to layer their SPF, so some in moisturiser, light layer of sunscreen, more in their primer, foundation and powder. But I've also seen people saying that different sunscreens might not work well together/actually cause chemical instability of some sort. No idea if that's true.
Australian Gold (oddly enough it's not actually Australian) gets mentioned too, and an Asian sunscreens are also popular.
If retinol irritates your skin you might be happier with a mineral sunscreen.