Buying a truck for carrying my kayaks

Hi!

So I've been carrying my kayaks on my station wagon roof rack and apart from tiredness when I'm out with my two sons, it's been working well. Lately, the need for a pick-up truck has come up and now I'm thinking about how I would transport my kayaks (up to three) in the bed of a pick-up truck. I have never owned a pick-up truck before so pardon my ignorance as I ask for advice and your feedback on my thoughts:

I would need to buy a used pick up truck that has at least an extended cab with the jump seats in the rear. Having said that, how long of a truck bed do I need to carry 12 - 13-foot kayaks?

The smaller pick ups seem to have about 5 ft long beds and with the tail gate down, would I be correct to say there would be about a 7 ft long floor where the kayak could sit on? If so, would that be enough?

I searched previous posts on this subject and it seems that some buy a bed extender that connects to a hitch. How much more support do you get in length with a hitch connected bed extender? And is it necessary?

Also, how do you guys secure your kayaks while driving when the tailgate is down?

Does anyone have any suggestions/recommendations on pick up trucks? Preferably automatic and it doesn't have to be AWD/4 X 4. I'm looking to spend up to $5k.

Many thanks in advance for your advice and input.

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You can easily extend the length of the truck with an extension bar off of the tow hitch.
I carry up to 3 kayaks in the bed of my truck do exactly that.