Would I use who or whom in this scenario?

I know there are numerous examples of who vs whom. But I can't find anything that really makes me feel confident in how to write this.

The sentence is

The two most important are the satisfaction level of the person whom
opened the ticket and the number of days a ticket was open.

I broke it down so I could use the He/She/Him/Her test. What I came up with is

The ticket was opened by her/him.

But that doesn't really match the sentence structure at all and really just rearranges it such that I can make that particular substitution. I could, if I wanted, rearrange it as

She/he opened the ticket.

which also works but still doesn't follow the sentence structure.

I suppose the best way to really clarify it is to say

The two most important are the satisfaction level of the person by whom the ticket was opened and the number of days a ticket was open.

Is that actually the correct way or are they both correct with the latter simply being less cumbersome than the former?