Upgrading from Bambino to BDB and wondering what are some accessories folks recommend? Naked portafilter, force tamper, etc.
(btw I'm pairing it with a Niche Zero grinder)

#1: Good coffee -- seriously

That will do more the the in-cup quality than any gizmo.

While I enjoy my high-end tampers, a well-fitting tamper is sufficient. One of the moderately priced square-to-basket tampers is a nicety on sleepy mornings, but hardly a necessity.

A bottomless portafilter is definitely useful for diagnosing problems.

If you don't already have a WDT tool and are pulling medium or lighter roasts, I like the LeverCraft and JKim Makes tools. I use the MATOW funnel because it has a shape that lets me see the grinds easily, doesn't extend into the basket and is heavy enough to sit on the rim without magnets.

I would not bother with "precision" baskets or shower screens. Many of the high-flow baskets can make shots worse, rather than better.

https://www.cafelatstore.com/products/breville-58mm
Cafelat silicone group gasket.

Bottomless portafilter.

WDT tool of your choice.

Portafilter funnel.

Scale of some flavor.

That should do it.

And, I would highly recommend ordering the 3 sizes of O-Rings necessary for bi annual preventative main.

https://smile.amazon.com/gp/product/B01 ... =UTF8&th=1

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

https://smile.amazon.com/Sterling-Seal- ... 11&sr=1-11

Not really an accessory, but good water! Whether you make your own recipe (rpavlis), use third wave water packets + distilled, etc just make sure you feed your new machine good, non-scaling water. This will prevent many of the maintenance woes people tend to report.

This applies to every machine, but I know the BDB struggles with the descale cycle so would recommend never having to descale in the first place!

All the other suggestions were spot on - enjoy your machine!