I am so very sorry. You don't replace your heart, but another grey can definitely heal your heart. You will have a place to put all that love you have for Blast. It will be received and treasured, and in time, that love will be for Blast and for your new pup.
Run free, Blast.
Over the course of 20 years with only one grey at a time I have had $500 years and $15,000 years. Cost averaging with supplements, insurance, vet visits, ER visits, dentals brings it to about $1,500 per year. Worth every single penny.
I am sorry to hear about your own health issues. I have no advice about Ava although the panties sound like they might be a good idea as long as someone could change them for you so you stay away from the fluids. Sending lots of good thoughts and prayers.