My DME supplier uses the Salter Labs brand of hoses and cannulas. They make many different lengths and nose tips, along with other O2 accessories. Here is one site which describes the specs of each product along with an idea of pricing if you wish to purchase from a local medical supply store or online:
https://www.directhomemedical.com/manufacturers...
This brand is hospital grade and reliable. Take care.

I don’t like the ones my supplier has so I order mine through Amazon. It’s trial and error and there are different types and sizes. I dispose of them once a week.
When I first went on oxygen my hubby would wash them & hang them to dry until we found out we could order them. Lol

Lincare supplies my concentrator and the tanks I use when I leave the house. They also supply the cannulas, so you should ask your supplier, as these items may be covered by Medicare, as I've never been charged for them.
I like a 4-foot cannula when using the small tanks and a 7-foot cannula when I use the concentrator.
When using the concentrator around the house, I like the shorter 7-foot hoses that I connect with swivel connectors as it's easier to straighten the sections out when they all get twisted. The 15-foot lengths get twisted far too easily.
The cannulas I use are a soft plastic where you put it around your head and I've never seen any that have different sizes for the section that goes in your nose. However, the ones I get are fine for me.

I use softhose.com to order my canullas and hoses. They are expensive, but the most comfortable and the hoses don't kink and deteriorate as quickly. As for canullas, I don't know that there's a standard, so it probably varies by manufacturer; leaving you with trial and error. Some folks to trim the cannula end off if they're too long.

Good afternoon Jane
I was advised when I got my first portable to use them for 1 week and then dispose of them. The ones they provide get hard in about a week so that works for me. They are short 3/8 inch with a slight curve to then.