My new phone uses a nano SIM, unfortunately.

Should I want to stick it back in my Jolla has anyone got any experience with SIM adaptors in a Jolla?

sim adaptors are okay

I thought id try and be safe and put it in without adaptor, but it needs to be full size to trigger the little switch in the top corner.
I just remember to be extra careful when removing it.

I have a nano sim adaptor in my Jolla. It was quite difficult getting it in there the first time, I was almost certain I was going to break the phone. I've taken it out several times since with no problems.

I really have to urgently warn against that, this is why my Jolla is now WiFi only.
Ask your MNO for a new SIM.

Yeah, SIM adaptors are a bit of a hassle. Currently have a nano SIM in a micro SIM adaptor which itself resides in a normal sized SIM adaptor lol. (since my Jolla is out for repair again, I have to rely on my trusty backup phone which still has a normal sized SIM slot)

Just don't do what I did

I used my nano sim from my other phone to test out the Jolla using a sim adapter. Worked fine. When finished, I took it out and put the nano sim back in the other phone.

Then, not wanting to lose the tiny sim adapter and to keep it handy for the next time, I popped the adapter back into the Jolla. As soon as I did it I realised that the 5 sprung contact pins had locked the adapter into place, springing up where the nano sim would have been. Took me about an hour with a slim metal tool to disengage the contact pins and free the adapter....

just put your adapter under sdcard and close toh