exporting my timeline without compression

[Duke Sweden]

DNxHD codec, for one. There are a few lossless, uncompressed codecs available in Media Encoder (as well as Premiere pro).

Dell XPS 8920
Intel i7 core 7700 build
GeForce GTX 1050ti
32 Gigs of RAM
3 7200 RPM SATA Drives
Windows 10 64-bit
Premiere Pro CC 2017 v.11.0

[Ann Bens]

Whatever codec you choose: Youtube re-encodes.

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Adobe Certified Expert Premiere Pro CS6/CC
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[Daniel Waldron]

Pro Res or DNxHD are supposed to be visually lossless, but are actually still being compressed into their respective codecs. Quicktime Animation or TIFF sequence are technically lossless, but will give you massive files.

[Jorn Bergmans]

Exporting your timeline to a codec that is truly uncompressed is very inefficient in most cases. (They produce giant files)
Depending on your source footage, and the way you handled these files during postproduction, your highest quality is whatever your highest workflow setting is. So, for mastering, ‘all you need’ is a high enough quality codec to keep your data and ‘look’ intact, so that file can be used to create your deliverables.

As mentioned, the best options for this currently are codecs like ProRes422/ProRes4444 (Apple) or DNxHR (made by Avid, good mastering codec for Windows based sets) – these codecs are technically lossy (but visually barely noticable), but will give you an optimal mix between high quality and decent file size.

As Ann Bens mentioned, YouTube will always re-encode your file. To save yourself a lot of upload time, there’s a few tips in the upload specs.
https://support.google.com/youtube/answer/4603579?hl=en
I’d recommend reading the much clearer Vimeo specs, too. They are good to keep as a bookmark!
https://vimeo.com/help/compression

My suggestion would be something similar to this for HD video:
h.264 – main/high profile, level 4.1, 12-15 mbit/s VBR 1-pass
aac audio, 160-192kbps, 48kHz (assuming this is what was mixed), stereo
This would be an .mp4 file – under the h.264 format option in the export settings for Pr / AME

I’d suggest exporting a master file (ProRes or DNxHR), then encoding that file to these suggested settings before uploading the .mp4