For EU citizens, 21bitcoin is an excellent app for dollar-cost averaging into Bitcoin.

With the code STACKSATS21 and a savings plan, you only pay a 0.79% fee, making it one of the lowest fees in the EU (lower than Relai).

Additionally, they have a fixed withdrawal fee of 1000 sats, so you don't need to worry about high network fees. Moreover, there's a feature that automatically sends your sats to your cold wallet once a specific threshold is reached (e.g., 1 million sats), which is great for UTXO management.