Oh Dear!
As others have said, there is no longer anything illegal about going out and about when you have Covid, if you are not feeling ill enough to e.g. stay off work. No requirement to test either. The view from the powers that be, is that now folks are vaccinated, Covid needs to just be allowed to go through the population.
My OH and I both had Covid in March this year. I barely had any symptoms at all. Was a bit tired for a couple of days ( explained away initially, by having travelled down South for a funeral and hadn't slept for 2 nights properly) had a runny nose followed by a stuffy nose for around 24 hours - (I have allergies) -and that was it. My OH had what we thought was a head cold ( and they always go into his sinuses and take a week or 2 to clear). We went about our business as normal before we knew. Only tested because a friend we had been to the funeral with, in a car, tested and was positive. Both strongly positive and I tested Positive for 10 days, in spite of feeling completely well after 2/3!! We did stay home, after we discovered we had it, but we are retired, so could do that.
That doesn't mean that some folks aren't more vulnerable than others, nor that some people won't be much sicker than others if they do get it. There are plenty of other viruses in a similar category - Influenza being one of them. I'm telling you this, because it is a guarantee that there will be lots of people out there with it, who have no idea that they have!
The only things I would say are
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If you feel worse tomorrow, you might want to cancel in case you are one of the unlucky ones who continues to get worse and it's no fun not having access to your own bed
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Your family members might catch it, and also be much more unwell than you, while away. Someone in the family might be too unwell to travel home on the booked day. So, have you got decent travel Insurance?
I don't envy you, your dilemma to be honest, but I'm not going to tell you to stay home and lose your holiday. You just need to weigh up the risks for yourself and your family. I don't think you are being selfish to others if you go, because as I already said, loads of people will probably be on the plane, who have it and don't know and catching a virus - any virus- is a constant hazard with airflights