How much more difficult is it ?
Depends on who you ask.

My first two models in the late 1970s were double planked and I was proud of how they looked. Then, like you, I wanted to frame and plank like a real ship. 50 years later and never did a double planking after those first two. I WISH we had the information back then that we have so readily available today, you are lucky.
There are many considerations from spacing of frames or bulkheads, to budget for high quality wood, to patience, to covered bottom (paint or copper) , lack of fear of do-overs and the list goes on. I think most would agree that the bow area is the most difficult. I am anxious to hear from members who have used both single and double planking why they prefer one or the other.
There are a lot of things to consider, but perhaps the easiest thing is to study a couple planking tutorials on lining off the hull and making the individual planks.
If you are going to spile the planks, the tutorial
A Primer on Planking by well-known author and ship modeler David Antscherl is great (PDF attached) I have since relied more on the method of hot air edge bending, but both can work if you are diligent.
Edge bending video by Chuck Passaro.
This is part one of four.
Perhaps the easiest single thing to look at to help you decide if you want to give a go at realistic planking is to study planking expansion drawings. There are a lot of drawings on the RMG Collections site available for free download. This will show you the shapes of the planks when they are laying flat. If this complexity does not worry you, go for it. One example follows.
