You would think a few buckets of some surface treatment on that decking you just replaced would make them last a hell of alot longer than they usually do now. Just a thought. I know it only took me only. oh... 25 years to generate that particular thought.
Think about Southern Yellow Pine,find a saw mill or lumber yard,tell them what you think you will need,if it is T&G the saw mill can make it up for you,probably half the cost of hard woods.when installed apply a waterproofing product like Thomsons once a year.
Pine won’t hold up worth a flip. Apitong is the best, but that stuff is expensive. We use white oak, not as good as apitong, but I can get it for about 1/3 the price.