It would depend on your business. I would think with this domain name that a .co.uk will be better as .org.uk implies an organisation such as a charity.
However, if all of the others are gone I would be inclined to look for something else because inevitably your domain will get confused by some as being the .com and you will lose custom.
When looking for useful sites I tend to look at dot co first and then look at the others. It can be very frustrating, but it is worth the time in searching for the correct name.
Is there a different word you can use other than my e.g best, good, choose. I looked in a thesaurus for my last domain name and came up with some more ideas.
Are there any other keywords which you are planning to use, which may fit.
Thanks. My research shows that a lot of people search for this keyword so I am quite keen to have it in the domain name. Accountingbasics, are you saying mykeyword.co.uk might not be as good as bestkeyword.co.uk?
When I have been looking for Domain names for our own sites, some of the domain tools come up with suggestions, one which I have seen again and again is adding 'my' in front of the original idea.
That was the only reason I was suggesting trying other ideas. When I saw it I had presumed that is what you may have done.