How do I find a proper mentor within my company?

First, I recommend this other discussion around finding a mentor which covers (and agrees with) some of the tenets of your question: "How do I find the best mentor for me within my company?"

Moving on, I think #1 and #3 are 100% correct, but I actually don't agree with #2. While a mentor outside your org can work, I haven't really seen the bias thing come into play (a good mentor should be honest no matter where they are in the org chart relative to you). This is why I heavily prefer having a mentor from within your org, ideally within your own team:

1. They can be tactically helpful - Closer to you means a higher chance of having worked with the tech stack that you're working on. While a mentor, especially for a senior engineer, is going to be more high-level and about behaviors, having a mentor that can help you with code helps a lot, especially if you're newer to the company.
2. They understand the culture of your org - In a huge company like Uber, there's bound to be sub-cultures across orgs, which means that different things are going to be valued when it comes to engineering performance. Since they're familiar with the culture, your mentor can help you pitch your work and behave in a way that's conducive to the org's culture.
3. The incentives are way better - Local impact is almost always better recognized than vague, high-level impact that applies somewhere across the company. Let's say I'm a Staff engineer on your team, acting as its TL. It makes a lot of sense for me to mentor you as I can directly work through you to achieve impact. It makes less sense to mentor a senior engineer in an org on the completely opposite site of the company as I can't work through them - It's also harder for me to achieve a concrete delta there as it will be harder to understand what their life is like.
4. Manager alignment is easier - It is vital for whoever is mentoring you to stay in sync with your manager, so they can give you the proper projects and grow you in a way that fills in gaps in your team. This is obviously smoother if the mentor is on your team (having the same manager) or on a sister team (probably knows your manager well, especially as this mentor is probably Staff).

Related resources:

• [Case Study] Mentoring Junior SWEs [E3] to Senior [E5] In Just 2.5 Years At Meta - It's more from the perspective of the mentor, but it does cover the mentee's angle as well
• "How do you get the most out of mentorship?"