I'm currently isolating after contracting Covid
I'm very sorry to hear about that and hope that you are feeling well, and haven't been too inconvenienced by having to isolate.
at my Christmas 'party'... 🙄
Surely you, and everyone else who is convinced now that it is their party to blame, must understand that it's not definite that you personally caught it at the party, even if there seems to have been a confirmed mini-outbreak as a consequence. And that you may have been the one to take it to the party, rather than catching it from someone else there.
Not saying you didn't but it's not clear cut at all if you did. Unless you isolated the whole rest of the week and you/your family didn't go to school/work/shops/anywhere in that time.
I think that, other than following the new regulations, everyone needs to do their own personal risk assessment with regard to whether to go to parties or anywhere else and whether to wear a mask (if it's not mandatory). And stop grumbling and micromanaging every else.
Clearly the government only want to slow down the Omicron wave (by slowing down parties and office travel and so on) while they get these jabs rolled out, rather than to bring the country to a standstill and decimate the hospitality sector again with another lockdown. So, some people will go, some won't, and hopefully that objective will be achieved. Those that do carry on going about their business are not in the wrong in this scenario.