Oh, OP.
How does your partner feel? Some people are ready for a new dog very quickly after they lose one. Others can take years. And that's okay.
IME if the breed is different it's easier to note the differences. That's the key. Note the differences (even if it's the same breed).
And remember, your new dog isn't a replacement so DO NOT feel guilty (because you will instinctively want to). Focus on the things this new puppy will bring to your life and look forward to the times ahead and take some time (even if that means walking away from the puppy every now and then) to remember the dog you lost.
If your partner is copying better, it is 100% okay to leave the training etc to him. Perhaps start with just giving the puppy cuddles when it's tired and having him on your lap? Do the gentle/easy bits first rather than diving straight in.
If it helps, I got a new dog once within a few weeks of losing one of mine. And I did cry. I cried a LOT. And I regretted getting her. But, within a few weeks, I loved her more than I have ever loved any other dog. I poured all my grief and the things I couldn't do with my other dog (or regretted doing, like making him sleep on the floor) into making sure the new dog got everything she could ever want. The fact that you already say 'who really is very sweet' indicates that you do already feel some sort of affection for this puppy. Time will be key here.
Someone will be along with more advice soon, but I really hope mine helps!
Edit: and of course it goes without saying, I am so sorry for your loss.