You can still do it but the procedure is different.
If you are doing this on a commercial scale and it’s going to be your source of income, then it’s not a local authority licence that you need but you need to be registered with the gambling commission.
As it is, it is purely chance as to whether people win or not. There is no element of skill. People don’t have to be geniuses because the questions are usually relatively basic although not necessarily obvious.
Here is the Gambling Commission website.
the grey area with what you are doing is the cost of what you are selling. If you were simply selling these items at the normal price and whether someone gets a prize is incidental to them then you don’t need a licence.
If however what you are doing is in effect selling a ticket (dressed up as something else) to potentially win this hundred quid voucher, then the people are actually betting because they are actually betting on which one of the items (the bath bomb) is going to be a winner. There is no skill involved it is purely chance.
It still gambling if whatever it is in each product has a different value in exactly the same way that people who bet on horses bet with different odds.