The importance of tube matching depends on the circuit design. If the tubes run at fixed bias and you can bias them yourself, it is not as important. It is important that the two phases of the output transformer have the same DC current, since push pull transformers saturate rapidly when there is an unbalanced DC current present. Allowing this condition to continue for a long time can result in permanent magnetisation of the transformer core. If the current bias is balanced, the differences in the plate curves of the tubes will only result in increased distortion. It is probably impossible to match the curves of 12 power tubes.
If you are seriously into tubes, investing in a tube tester/curve tracer is advisable. I use this model:
https://www.essues.com/etracer/index.php. If you know the operating condition of the tubes in your amp (plate voltage, grid voltage), you can measure the plate current at that point. You can then sort out the tubes into two batches of 6 to try and match the total current of each batch. You can also try to match the plate curves, but I suspect this will be a futile exercise. The machine also allows you to determine useful tube life remaining, gas leaks and other problems. I find it is better just to buy the tubes myself, sort them out and throw out the substandard ones. Even buying from the manufacturers does not guarantee you will get good tubes, and problems can develop only after a certain number of hours of usage. Without a tester, you will end up replacing all the tubes every time a problem arises. If you use tubes for your preamp and especially your phono stage, you would want to test the tubes and pick the ones with the lowest noise and microphony. I use a George Kay small tube tester for this purpose.