Im so sorry for your loss, I was in a very similar situation a few months back so I will tell you what I ended up doing
My boy Quill passed after surgery and I was left with his brother Olly, they were both only just a year old and Olly is and was still very healthy so I knew I couldn't just leave him alone. I took a few weeks to heal both Olly and I, I looked up many different ways I could help him and I found that if the other rat saw and smelled the body for a few minutes that helps them process quicker so that might've helped Tia. I spent most of my free time with Olly and holding him and playing with him in every way possible to try and keep him company while we both grieved, and I bought a small radio and had music playing while I couldn't be around him so he would still feel as if people were there and I cut up old clothes of mine and put in his cage so he could smell me around him. After about 3 weeks I found a pair of young girls at the same place I got my boys. While I didn't feel entirely ready I knew Olly was and I didn't want to put my grief on him and this being exactly what my vet recommended with Olly being neutered. I felt as if i was replacing Quill and sometimes I still do, but I love my girls and Olly is so happy now and has done so great with the girls hes acting like hes only a few months old again.
It hurts really bad and I see you just joined so I'm guessing you're a new owner and this caused you to join this forum which is exactly what I did hours after Quill died so this is what I wanted someone to say to me. There is no right or wrong way to handle this situation, every person and rat will handle it differently but you will give Tia a good life and it will get so much easier as time goes on I promise. You just do what feels right, this purely is a just trust your gut situation where you decided what is best for the both of you, you guys are in this together and you will get through it together too