ᐅ Notched trowel / tile adhesive: What do you recommend?

Hey,
we are about to start tiling soon. Porcelain tiles 30x60cm (12x24 inches) on underfloor heating.
Which notched trowel would you recommend—8mm (5/16 inch), 10mm (3/8 inch), and which tile adhesive?
We were thinking about flexible adhesive from Knauf. Is that okay?

Best regards
Bollermann

For the measurements, I used a 10mm (0.4 inch) spatula. The adhesive is from PCI, the Nanolight. It is very easy to work with.