I created my own keyboard layout. It is probably to small for you, too, but here you find a tutorial if you want to build your own.
On PureOS Dawn it is no issue any longer. Scaling is fixed. However, in Dawn Squeekboard will be broken entirely, Phosh dropped the support in favor of Stevia. There is a chance Purism will pick support of Squeekboard, otherwise Stevia has no such issue with scaling.