How do you order a new sim these days

I try looking it up and there is nothing easy to find online. We all use sims in our fones. Used to be so easy to get one sent to you if you needed.
Can't really find anything helpful. Especially in these times of the virus. We need to be able to get a sim easily if we need it.

I will be getting a new phone in the future cause badly need one. My phone hasn't been displaying signal for weeks so went into sim status and my phone number, network is unknown. Signal strength is 0. Unknown mobile network type. Mobile network state is disconnected.
I have another fone with a different number which is fine. Signal is great.
If I get a new phone I need a working sim.
Obviously this one isn't working. Need to order cause can't really go into a shop anymore to buy a sim not for a while. So where do you find one?
I'm after hunting around can't find any.

I think the sim I was using might have expired.
I'm still fine using the WiFi but I'm not connected to the network anymore.
I got a text about two weeks ago which scared me a bit. I hadn't topped up in 8 months cause I don't really need to anymore.
Said if I don't top up within 7 days I will no longer be able to use the services. That very morning I topped up. Just so I can keep being able to send a text if I need. I topped up within the time limit but now everything is disconnected from Vodafone. So I don't know if that had something to do with it.

Where do you get a sim card online?
Don't say vodafone. I checked it out and you used to be able but the link and page is old and you can no longer do that online.

I just need to know I'll be able to get a sim card when the times comes
Thanks for reading all that