How wide should my first anal dildo be? I’ve already used buttplugs.

The buttplug I currently use is 2.8 cm at its widest part. It’s beginners’ plug, and I take it easily.

Now I’m thinking of buying a beginners’ anal dildo, and there’s one that’s 2.9cm wide, and another bit bigger that’s 3.3 cm wide.

Should I immediately go for the 3.3 one and do slight stretching out? I feel like 0.4 cm isn’t that much. I doubt the 2.9 will help me with training as it’s so similar size as my current plug. Or are dildos different in anal?