When should I start booking the SHA hotel and Thailand Pass application for my trip to Thailand?

I am arriving on the 15th April and already submitted the Thai Pass application.

I am looking forward for the Arun Riva Bangkok!

It's facing the river and from the balcony we can see a monument. We expect to be able to drink some wine in the balcony, looking at the boats and the main monument on the other side of the river (diagonal) 🤩

There is a more expensive hotel facing the monument and the river, but I am ok with this angle and loved the price!

I know next day I can walk to the main monuments too, as traffic there seems chaotic

You do know from April you no longer need a pre departure PCR Test in your own country UK

Start now. You need to have a flight out within 30 days. The hang up would almost certainly be with your airline not allowing you to board without one. Best option is a changeable ticket. Alternatively Google “onward ticket” and you’ll find lots of companies that will sell you one for $10.