Mobile short-term contracts

My nephew is moving into a rented flat just outside Newport Wales, in a few weeks' time and needs to find a way of setting up some broadband. Long-term contracts are out of the question right now. Unfortunately he doesn't yet know whether the property has a landline, so until the technicalities can be sorted out for that, it seems that mobile broadband is his only option. I understand no-one does short-term fibre so that's out as well.

He's a programmer and needs to use a laptop screen-size for his private research work...so relying just on a smart-phone for everything isn't going to be good enough. He also downloads quite a lot of stuff, so data usage is quite high (I don't know what, exactly). Does anyone have any recommendations for a mobile provider, short-term (say, for a couple of months) while alternatives are being set up? I am passing to him an unused TP Link MR6400 router, which I believe is a good one for 4G mobile.
What I've checked out so far indicates that Three Mobile might suit; but I have no experience myself of mobile broadband so others' input would be useful.

All depends on the data usage level.

The VDSL2 (?fibre) services and Virgin Media are available on 1 month contracts

https://www.thinkbroadband.com/packages and select 0 -3 months contract filter

Most important consideration at this point will be to find which mobile network works well in that location, indoors.

EE, Vodafone, Three, and O2 are all worth trying using a PAYG SIM first before signing up to any longer term contract.

Pulse8 broadband do 1 month fibre contract

Hello, thank you all for those thoughts and links....hadn't spotted the packages section on here, although have found others. Had never come across Pulse8, could be useful....my nephew is on low-ish pay, so has to watch the pennies.

I'd jump on eBay and buy an unlocked 4G EE router, I picked one up for £30 and then pick up and loaded SIM (for example found an EE 4G sim for £15)

This is of course if the the coverage is good in the house, I've used this method when I travelled round the UK and needed a short term data connection and didn't want to tether my mobile.

Three, EE and giffgaff are probably his best options, I found giffgaff to be slow but usable.