Hello @Cosmic_Curiosity,
Iām sorry to hear your partner is having a rough time with their depression. I think they are very blessed to have such a loving and caring partner such as yourself at their side to help them through it 
The essential oil blend you posted (just adding in a link for easy reference, it really is a lovely mix!) is a great start, and I agree with Brandy that a spell jar is another great option!
I think anything you make that they can carry with them throughout the day to remind them of your love and care would be a great option. In addition to a spell jar, you might consider enchanting a piece of jewelry- either something you or they already have, or a newly crafted piece.
Here is a guide on how to enchant a piece of jewelry- you can enchant it with whatever intention you choose, such as happy thoughts, anti-depression, self-love, positivity, general good energy, etc 
Another option is a worry stone. Sometimes when negative thoughts feel overwhelming (I have anxiety and get the anxiety thought overload at times), having a worry stone is helpful. This is just a smooth stone or crystal you can handle that helps release negativity and work through tough mental states.
A worry stone can be anything at all- I have some beach rocks I use sometimes. If you have them around, some stones are particularly good for helping to ease negative thoughts and replace them with motivation, good energy, and positivity. Here are a few:
Wishing you and your partner all the best- while Iād say I hope you can find the perfect thing to help them through this tough time, I already know they have the perfect thing already by their side- you!
Hope they are feeling better soon. Many blessings! 