Treat it as part of the holiday and have fun. Even though you will be sitting on the plane for ages, do leave yourself loads of time at the airport. I love browsing the shops and having a drink or meal, and people watching. A flight to the West coast of the US (8-9 hours) was never long enough for me as there is not quite enough time to fit in three films, so I either had to stop one in the middle or fill in with shorter films and TV programmes.
There are lots of people giving advice for long haul flights on YouTube - often contradictory. Neck pillows are controversial. All are unanimous that the trays and seats need a good rub down with a disinfectant wipe as cleaning between flights is not as thorough as you would wish, as time is at a premium between flights.
Also advice on YouTube from flight attendants is unanimous in that you should be nice to the staff - on the ground and in the air. If you are pleasant and well mannered and not pushy and demanding they will be more likely to grant you perks. I don't think (but I'm not sure) that asking for an upgrade on check-in is the done thing but it's worth a try, especially if you don't make a fuss. But that is obvious really.
We have twice been upgraded, but this was not of our own doing. The first time our flight was overbooked and we were offered an upgrade and a substantial compensation if we took another route. (We accepted but they lost our luggage in the changeover.) For this to happen it might be best to check in at the desk quite late, but that is of course also risky.
The other time I was flying from San Francisco back to Frankfurt. I was on my own, like you, and economy was full but there was a single spare seat in business class which I was allocated for no extra charge. Luck of the draw really.
The YouTubers also recommend lots of gadgets which make things easier - a cradle to hang on the seat in front to rest your feet in, various holders for phone and tablet to watch your own downloaded films, and things to hook on the seat to keep things handy. Also various tips such as: keep the most urgent things in a smaller pouch on top of your bag in case you can (or are even asked to) put the carry on bag in the overhead locker . You can then take it out and have it with you. (Hand cream, glasses, medication, your documents, disposable flannels, toothbrush and a comb, and the spare knickers mentioned above should also be handy for the freshen up half way, whether you do this on the plane or at the stopover airport.)
WiFi is in my experience not reliable on planes, but you should download the airline's app at home before you leave anyway. You can familiarise yourself with it, plan your menu and see what meals are on offer, see what entertainment is available and how to watch it. These days there is a USB port by your seat to charge your gadgets.
If you are bothered by light and sound and would like to sleep, by all means take earplugs and an eye mask.
On YouTube I have also seen warnings that the pillow and the blanket (if provided) are not necessarily clean but that doesn't really bother me. I would just cover the pillow with a scarf (another indispensable accessory) and the blanket isn't really touching your face anyway.
Remember to pack your passport and cards in an RFID protected pouch or wallet and be aware of data theft, and to print out your boarding ticket just in case (I've always used the one on my phone but have the paper one as back up)
Most important is to check the airline's baggage restrictions thoroughly and any other advice they give regarding checking in, upgrading , flight information etc, as this will reduce stress at the airport. You can check in online at home before you leave.
Sorry if I've covered too much obvious stuff if you are an experienced flyer. I haven't flown myself since the pandemic and I know a few things have changed since. However I do recommend looking out the advice on YouTube; you can certainly pick up some tips there. Many of them are American and concentrate on the American security system TSA but you can ignore or apply as necessary. I formation regarding the security check is nothing to do with the airline, you can gen up on that on the airport's website.