isoflurane is usually the best way to anesthetize rodents, it has many advantages compared to ketamine/xylazine injections and other chemicals. Recovery is very quick and you can adjust the flow and percentage in real time.
For euthanasia, the best way might be depending on your institution IACUC's protocols. I know that the preferred methods in France vs the US differ quite a bit in my area. All of these questions could be asked to them as they will provide approval of the animal protocol and useful advice for you in specific settings.