Purina Pro Plan is the one we use the only problem we have is when we forget to but some and have them eat something of lesser quality then the toots and soft stool commences. There are many coupons available for it too I know it’s costly.
I would try a water retrieval dummy toy. The floating orange stick or there is a duck shaped sling-shot by Hyper Pet. Sticks might not be enough of an interest. Also the more the merrier as per usual. Bring your trunks haha.