Well it depends on how your finances are generally and your tax rate - you might keep less than half the bonus if you're a higher rate tax payer with student loan repayments for example.
But if you want to earmark some of the bonus towards the dressing gown, that seems reasonable.
Then you could put the rest towards a weekend away. I assume that this bonus isn't the only money you have available for non essentials so it's likely you can afford to top it up from other money?
If not, you would be much better having a smaller treat for you/family, then saving most of it so you have a bit of an emergency fund.