Here's a few comments from me regarding comfort, all IMHO as what I've found to be the case, I'm sure others' experiences will differ.
Sleeping aboard in a harbour is generally very good because of the shelter and the gentle swaying of the boat is actually comforting and enhances sleep. Also, the boat is, or should be, secure so no background worries about anchors, wind direction etc.
Camping wild on the boat is a different story and comfort will depend almost entirely on the weather and sea conditions - primarily the wind and it's direction.
In calm conditions which are lasting then there is nothing much to be concerned about except you set the anchor well and you've plenty of depth at low tide on the shallow side of the boat and the anchor light is on. (A bright garden type solar light will do well for the few hours of darkness in the summer months and it'll remove a battery drain issue if you've not got much power reserve.)
In a breeze, even a force 2 to 3, you could end up sea sick or have a bad sleep if where you choose to stay is not the best. Firstly you need to anchor well and be absolutely certain you're not going to move, secondly you need anchor room because there's every likelihood that the wind will swing you during the night. Neither of these will make you physically uncomfortable but if you're unsure, you'll sleep lightly.
Where you anchor will have a bearing on your physical being and, as a few folk have indicated, sea sickness is possible even on a small swell if you're under cover or have to undertake tasks aboard without looking out to sea. A typical and attractive anchorage in a small bay may or may not be a good choice, it could start off very pleasantly but turn bad on a wind change, the converse is also true. The reason is to do with wind direction and wave direction and they're frequently not the same, especially in sheltered areas. Lets say you're lying to a good anchor in a secluded bay at the back of an island, no one else is there and the wind is just an offshore breeze - sounds idyllic - maybe aye, maybe no. There will likely be a swell from the ocean which will come into your bay from offshore so contrary to your wind waves, the strength of this will depend on the weather preceding your arrival and it will be coming at you from the stern. The wind waves will wrap around the island by diffraction and will probably not enter your bay square on, worse still, you may have these waves wrapping around the island from both sides! So now you've got a light head wave train, a diagonal wave train from left and from right, probably out of sequence with each other, and finally you've got the overall slow swell coming from your stern. Very sick making! You could be better off in a more exposed location with a stronger exposure to the breeze but fewer cross waves to rock and roll you.
Plainly you can have any or no combination of these conditions so it's very difficult to assess before you arrive at your chosen anchorage.
I the wind picks up to a 4 or 5 you could have a very bad night or simply leave and look for better shelter.
I have no water bound solution for this but simply pass it by you since if you've not done it, sitting in your planning armchair you'd be forgiven for thinking differently.
A rib doesn't tend to have the slower motion of a larger boat or a sail boat but it does respond to pretty much every wave passing by. If it chops up a little from the side you'll get slapped by waves and they'll likely splash aboard too.
If you find yourself inadvertently in a poor situation, it's not unreasonable to lay your anchor a little offshore, beach the boat and tie it off to land and sleep ashore, you'll get a few hours sleep while the tide rises or falls and comes back to the same position at which time you get back aboard at least a little rested, or possibly very rested depending on the state of the tide. Plainly you do not do this at time of high tide!! It may not come as far in on the next tide and you'll be stuck for a while! On the plus side, you won't be sea sick.
Finally, in no way am I suggesting not to do it but be aware it can vary from a simple exercise to quite a handful to manage.
