Lot of misinformation on here…
Not surprised your accountant can’t help, they aren’t regulated to give financial advice so aren’t covered to give recommendation as to who to go to and how to invest. They’ve done a good job in suggesting making a contribution as end of year tax planning IMHO.
SIPP should be able to set up very quickly, you should still have time to Bacs a payment to the provider or CHAPs if needed very quickly – is your company year end 31/03?
Lifetime ISA doesn’t open until open until April and also aren’t deductible against corporation tax.
Nest has annual limits on contributions at the moment – £4,900 I believe. Again not sure of how much you want to contribute?
As mentioned COMPANY contributions don’t attract personal tax relief.
Sorry if I come across grumpy, just trying to help 8)