I am almost done with the domain changes to this blog. It is currently reachable via www.danielschneller.com which is what you should already be seeing in the address bar right now.
The danielschneller.de domain is working partially, I guess some DNS updates have not propagated to everywhere yet. It should redirect to the .com immediately, however currently it still seems to have the CNAME to Blogger in place. This should only be a matter of hours now.
Mail is configured for both domains and seems to work just fine.
During the whole change process I had to contact DomainFactory's support for some tips on which contract types would give me the features I wanted at the minimum possible cost, and even though it was on Sunday I got a (sensible human-written) response within 5 hours. Pretty impressive.
Their web interface is clean and understandable, very nice as well. And the pricing is really affordable: I now have 2 domains in the MyMail package which is 6.60€/year per domain + the domain costs of 1x .de (6.60€/year) and 1x .com (12.60€/year), totalling 32.40€ per year. This is way less expensive than the 1&1 rate (47.88€/year for just the .de domain and no chance of configuring CNAMEs).
The only thing left now is to cancel that 1&1 account.