Realistically, no-one here is likely to be able to solve your underlying fear of flying. It's very real for a lot of people, and I do sympathise with the dilemma you're wrestling with. All we can do is give you facts and hope you can process them sufficiently to give you some assurance.

So ...

Please rest assured that the A350 is an extremely safe aircraft, and in terms of sleeping it's as good as anything in the skies right now because of the cabin pressure and lighting. It's as close to a natural environment as you're going to get in the air - certainly way ahead of two of your preferred aircraft of 747 or 777. It's also a widebody, so with modern aircraft design you'll feel that's there's a great deal of space around you.

You'll be travelling on a major airline with a very competent regulatory body. There isn't going to be any skimping on maintenance to reduce costs.

It seems you feel more comfortable with four engines because you think the risk of all of them failing is less. That's understandable, but two engine aircraft have been flying over stretches of water for many years without any issue. They have to be rated to do that, and the airline will have a mapped out diversion plan which covers every eventuality including medical emergency and aircraft defect. Even if something goes wrong with one engine the plane will happily keep flying on its remaining engine to reach the diversion airport.

The fact is that the most dangerous phases of flight are take-off and landing - so actually in terms of risk you're far better off taking a direct flight rather than a series of shorter ones. The number of instances of planes failing when at cruising altitude is infinitesimally small, and even for those that do they enact the diversion plan. All pilots are well versed and extremely skilled at getting planes safety on the ground even when they develop a fault, and they practice every scenario you could ever think of in simulators. One of the hard things is accepting that you're not in control and are relying on others to get you to your destination, but ask yourself - would you rather be in charge of the plane yourself, or have someone with massive training and a large number of flight hours/experience piloting it!?

I suspect the reality is that you'll sleep for much longer periods than you believe and hopefully there are enough distractions during the journey with meal services and movies on the IFE that your mind can be distracted by what's happening outside.

Finally, talk to the aircrew when you get on and let them know you're a nervous flyer. They really are well-versed in looking after people who do suffer from this fear and will be able to put your mind at rest. Planes can make strange noises (or indeed, in the case of modern planes because of the soundproofing, no noise at all, which can be more disconcerting) and they will be able to give you an explanation that maybe what you think is abnormal is really perfectly fine.