Best IPhone 6 waterproof case that isn't to bulky?

I need one that doesn't make my iPhone bulky and can also go a decent amount of distance underwater for a considerate amount of time. I'm thinking of buying the life proof case but I don't know how thick it is. Any suggestions?

There are NO waterproof cases. Only water resistant cases.

What you ask is too imprecise. Define "decent amount of distance underwater". How many metres/feet do you need to descend to? Define "considerate amount of time".

But any case which can protect the phone for more than about 1 metre deep and for over half an hour is necessarily going to be bulky as it needs to be strong enough to resist water pressure. Note that many cases which are water resistant quote figures which only apply in fresh water. If you need the phone to go into saltwater or into a chlorinated pool then those quoted figures will be reduced.

Just buy a slimline protector case of your choice, and when you need to go snorkelling deep down either switch to a bulky and rugged case with a very high water resistance rating or better still, just leave the phone locked inside your car or storage locker.

If you need an underwater camera then get a camera designed for the job: I used a Ricoh WG-4 to capture this image of an octopus about 3 metres underwater off the coast of Rhodes, Greece, just two weeks ago.

"Isn't so bulky" is subjective. What may be very thin to me may be a brick to you.

At least start by naming a water resistant case that you feel is too thick, and we can work from there.