I’m so sorry for your loss of Sparky. It’s quite common and normal for a budgie to be “depressed” after losing a best buddy. The good news is, birds don’t really mourn for too long. Sometime within a month or less, you should see Minty start to perk up and adjust to single life. You’ll find that some budgies do just fine on their own once they adjust. Give it about a month and see.
In regard to getting Minty a friend, remember, there is no guarantee that any two budgies will end up getting along regardless of age or sex. Any time another is brought into the home, you have to be prepared to leave them in separate cages just in case. Then of course you’ll need to observe a quarantine period for any new additions for 30-45 days.