How are you tracking your portfolio across so many exchanges?

I've only been in crypto the past 6 months or so which isn't very long but I already feel like I've lost grip with how much I bought, using what pairing and what my average cost is across multiple exchanges.

It's making me feel a bit uneasy. I'm in it for the long term and that's kind of the problem. How can I keep track of these things and will these exchanges even exist in 10/15 years if I don't keep track of the information myself? What happens in 10+ years time when I come to sell and I have no idea what my average cost was?

I hold all my crypto off exchanges so is there a tool out there to connect to that can sort it all out?