Kayaks are awesome. Forget the sit inside, nobody I know stays in one long down here.
Kayaks can get through skinny water often it is better to stay seated and paddle the mud - most yaks will go through 3inches of water you won't get that ability to skim over 1' spots like a pirogue but its still pretty amazing what you can get into.
From there the conversation does get real sticky. The Ultimate is a great kayak for up in the marsh it will feel familiar to your pirogue while being more stable and the seat is outstanding. If you expand from there and want to fish open water you have to keep a pump handy to clear incoming water.
Your height weight and size will play a role in what you like/want then its a matter of money.
There are many smaller kayaks that will fit neatly in the back of a truck but most of those you will not be able to stand and fish in. However you can either strap it down well or buy a bed extender to handle whatever you want.
Bobby Lynn's marina will be renting a variety in may, and Calmwater Charters in GI has the ultimates for rent right now. Shoot hire Capt Danny for a guided trip and he will show you all you need to know about kayak fishing, he also has 3 types of Kayaks made by native and heritage that you could try out.
We send plenty of folks this way so I have no trouble inviting you over to www.bckfc.org
to check out the kayaking forum.
Hope to see you on the water