I look after dogs for friends, colleagues and neighbours when they go away on holidays, sometimes for a few weeks at a time. You could even sign up with an agency and get paid for doing this. I am also a foster carer for the local animal shelter for cats and dogs, which are typically for a few weeks duration. Like you, I lost my dog not that long ago and have found fostering a good short term experience in the interim until I feel ready to commit to another dog. As a bonus, the shelter supplies all food, we just supply the cuddles! So far the animals through the shelter have been kittens and puppies, so I find them easy to give back as I know they will find homes very easily. There are also sometimes programs to look after pets for older people who have to go to hospital, or for women escaping F&DV that may want foster carers.
Another possibility would be fostering assistance/guide dogs as puppies. I have no experience with that, but the time frame would be for a lot longer - I think around a year. It might be hard to give up, but you would know that the love and attention you show the dog would be really appreciated by the person who would then receive a guide dog.