Make sure you get a laptop with a self-encrypting SSD that supports TCG OPal. This will give you maximum speed sector-level encryption. Read this post on my nerd-blog: https://vxlabs.com/2015/02/11/use-the-hardware-based-full-di... (no ads, no referrals, really just info) which explains at a high level how SSD-based encryption works.

The open-source msed tool has now been renamed to sedutil see https://github.com/Drive-Trust-Alliance/sedutil but it still works the same way.

It would still be possible for a sufficiently advanced thief to secure erase the drive (they need to know how to use TCG Opal to do that), but they will never see your data.