Might be worth asking Sparkplug of this parish,he's good at this sort of stuff
Kimbo
Thanks Kimbo
Others have pretty much covered the options.
1) Tether to smartphone
2) MiFi / Hotspot
3) Starlink
Tethering is great if you get a good enough signal on your phone inside whatever structure you're using it in. The more insulation and especially metal you have between your device and the signal the worse this will be. In my van it was terrible. The other consideration is the number of devices you need to connect. Tethering is OK for a small number of connected devices but starts to get problematic if you're trying to connect a ton of stuff.
MiFi / Mobile hotspots are the logical next step if tethering doesn't quite work for you. I have the Netgear Nighthawk M1 which suits my needs very well - but there are tons of these around including 5G enabled ones (the M1 is only 4G). Typically these have better antennas that smartphones built in - so you're likely to get better signal than you would with your phone anyway.
Adding an external antenna is the real game changer though - as long as you don't get one of the cheap ones which are pretty much useless. Expect to pay upwards of £60 for a decent one. One of the other advantages is that you can often connect a lot of devices to them (depending on which MiFi Hotspot you buy). For my setup I can have my phone, my work phone, Mrs S' phone, her iPad, my laptop, my work laptop, her laptop, my PiHole (don't ask...

) and a smartspeaker in the van at any given time. I also have it set up with a 'guest' network so there are quite often a couple of other people using my WiFi at events.
I use a Three mobile Unlimited SIM which is £16/month and I use it frequently enough to make it worth having a subscription. If you're only using it for a couple of weeks here and there then you can buy a PAYG SIM and pick and choose which network you want to use based on where you are. Three do an unlimited PAYG SIM for £35 or you can get 50GB for £20. EE do similar pricing, but don't offer unlimited and they cap the speed at 25Mbps. This stuff changes all the time so you'll want to shop around for the right SIM.
There are also Strongest Signal SIMs which are data only and will automatically pick the strongest available signal irrespective of the carrier. However, they're pretty expensive and would only really make sense if you were living full time in a moving vehicle or worked in Mountain Rescue or similar.
Starlink is next level. I have no personal experience of it, but even on the RV bundle which allows you to only pay for the months in which you use the service, it's prohibitively expensive IMO. Feedback from people who I know seems to be very good once the sometimes tricky initial setup has been completed and it is possible to modify it to work with 12v systems.
You could also look at Vsat systems as used on ships if you wanted, but they make Starlink look cheap
That's pretty much all I have to say on the matter other than there are also options to buy/build (Raspberry Pi) mobile routers that will pick up a free WiFi signal from somewhere else and let you connect to them securely through a firewall and a VPN. I've been tempted to build one for the learning process, but TBH I've never found myself in a situation where I really needed one. Good if you're in hotels a lot I guess, but then I just take my M1 and use that so...
Hope some of that might have been of use to someone.
