don't get anything thinner (which will obviously be more flexible) as that is the strrength of using flex pvc. What you do is get some fittings to make these curves. You'd cut and clue them in as needed. Use sweeping ells (street 90 deg ells and 45s) and not hard angle ones as this lessens your flow.
This is a great suggestion. Just use regular pvc fittings to make your turns. Remember, flex PVC fits into standard PVC fittings and uses the same primer and glue. You can buy all that PVC stuff at big box home stores or your local hardware store. It's very inexpensive.
Just like brokensword stated...they make wide sweeping elbows so there's less resistance. Believe me, with the power that these pumps put out, I doubt any turn will affect it much.
Unless you know exactly want you need, you're better off buying those fittings in a store rather than online.
You will not find a better hose. The flex PVC will be the last hose you buy.
But I will mention this: some people on this site use sump pump hose and have had very good results with it. So, if you really intend on sending back the flex PVC, get the sump pump hose.
Do not buy that "non-kinking pond hose". I love Tetra products, but that hose sucks and it's not cheap. It will spring leaks and split apart at the worse possible moment. You don't want a major leak. It could empty your pond.