I totally agree with everyone who has already spoken, you should NEVER EVER get a second bird for your current bird! There is absolutely no guarantee that whatever bird you bring home will get along with your current bird, or vice versa. The relationship that your current bird had with your bird that passed is not something you can recreate, and a lot of the time people go and get another bird that they wouldn't get otherwise, but like you, they think their current bird is "lonely" and remembers the relationship they had with the bird that just passed away...then when they get another bird home they hate each other, are violent with each other, and jealousy issues between cause your relationship with both of them to be strained.
My best advice is only get another bird when YOU are ready for one, when YOU want one, and then go for it. And if the new bird bonds with your current bird then that's awesome, but if they hate each other you can work with that, because you wanted to get the new bird and that's the only reason you have him. Your Ekkie is probably missing his mate, but he's not "lonely" as he has you...
And FYI to Cardinal, I've not ever heard anything about Budgies and/or Cockatiels carrying diseases that don't effect them but do effect larger species of parrots....Do you know what disease or diseases you're speaking of? I've been a Budgie and Cockatiel owner/breeder/hand-raiser for decades, and owned large parrots at the same time, and I've not ever heard of this nor had an issue, so I'm curious as to what disease or diseases you're talking about...