First, be sure your phone is unlocked. if you got it free from a carrier, it probably is not unlocked, and would not work with another sim or esim.
Lots of folks here like Airalo. Esim only. Pretty inexpensive. Cost more if you get an esim with a U.K. phone number, but you probably don't need that. You can use Whatsapp or Google Voice.
Myself, I like Roamless or BCengi. They are true Paygo (Pay As You Go). That means I give them $10 or $20 to add to my "digital wallet". This money never expires. As I use data, money is deducted from my digital wallet, at $1.58/Gb for BCengi, and $2.45/Gb for Roamless. Next year, I can use any leftover money for whatever country I visit. They each work in some 200 countries, but you would want to check what the cost / Gb is, as some countries are quite expensive.
In the past, I've used GiffGaff, and it worked fine also.