How do I symlink certain directories in /home to an SSD?

You can do it from a Live CD, but if you logout from a graphical session and switch to a virtual console using Ctrl + Alt + F1, you'll be able to move the folders too.

Your steps are correct, some expansion below:

1. Switch to a virtual console and login

2. Mount the SSD if needed, that can be as easy as:

   sudo mkdir /media/ssd-store
   sudo mount /dev/disk/by-label/YOUR-SSD-NAME /media/ssd-store
   

   You can use tab-completion after /dev/disk/by-label/. This only works if your partition has a label, otherwise you need to replace it by /dev/sdXY

3. create a folder that holds the files from home:

   sudo mkdir -p /media/ssd-store/home/jorge
   

   If you've a custom umask setting like 0027, you need to sudo chmod 755 /media/ssd-store. You can check your umask setting by running umask (defaults to 0022)

4. Change the ownership if needed, so the user can always create more symlinks if needed:

   sudo chown jorge: /media/ssd-store/home/jorge
   

5. Move the files (add sudo if you do not own /media/ssd-store/home/jorge):

   mv /home/jorge/.config /media/ssd-store/home/jorge/
   

6. Create the symlink:

   ln -s /media/ssd-store/home/jorge/.config /home/jorge/
   

Notes on the above: you should add an entry in /etc/fstab for automounting the SSD. Use sudo blkid to determine the UUID for your SSD partition and add the next line to /etc/fstab:

UUID=[uuid] /media/ssd-store ext4 relatime,errors=remount-ro,discard 0 2