any reason I can't make fish pie with soya milk?

[IHeartKingThistle]

And how can I up the tastiness a bit?

Not sure about using soy milk - aren't most brands sweetened in some way? How about making a sauce from fish stock thickened with a roux?

Well I made it with unsweetened soya in the end - it was fine, not as creamy as with milk but the kids liked it and I could actually eat it! So a result!

I have seen many fish pie recipes with coconut milk, that would make it creamier.

Try using the soya or Oatly cream instead of just the milk.
I prefer Oatly in savoury cooking personally, the kids will eat it regardless, but I'm not a fan of the taste of soya milk.