Hi,
You would only need to register for VAT in the UK if you are making taxable supplies over the threshold of £85000. You can see guidance here:
Working out whether you need to register
You will only be making taxable supplies in this scenario if you are the importer of the goods and the designated importer of record on the import declaration. If the overseas supplier is the importer of the goods then they will be making a supply to you in the UK and you will then be making a separate taxable supply to your customer in the UK.
If the customer is the importer of the goods then they will be responsible for accounting for the import VAT on the goods on arrival and because you will not own the goods in the UK you will not be making any taxable supplies in the UK.
You will need to arrange this with the overseas supplier.
Thank you.