What gas welder should I buy

I'm looking at buying a gas mig welder… I just have no idea what to get. It's not going to be used relentlessly just every now and then.

I bought a "Gasless" Mig, which can be converted to gas. Why have the hassle of storing Gas canisters and when you do come to use it find out you ran out of gas last time.

While I cannot argue with your experience I have never heard a good thing about gasless migs.  Buy a midprice, or top price if you are rich gas one and go to boc and rent a big argon cylinder or one of those hobby cylinders that don't charge rental.

Don't you need a licence for a large gas bottle though? Have you got one and is it any Good?

Ive had one (boc bottle) for 30 years, probably paid for it 20 times over with rental charges, but you only pay once a year and its easy to change an empty bottle for a full one assuming you have a boc dealer within reasonable distance.  No license required, just have to carry some paperwork in your vehicle when carrying the bottle.  Wouldn't suggest you rent one for so long but get it for a year or 2 and get stuck into the welding, can then get by with the small canisters for the odd job…