If you do not download the blockchain, you will need to trust third parties. Allow me to say that trusting third parties goes against the concept.
This has simply become the reality of bitcoin and it will become more and more normal the bigger the blockchain grows. And we will see no matter what a point where the blockchain will not fit on a normal device anymore.
Also if you need a different service to send small transactions then you are really trusting a 3rd party with a lot more then I am willing to trust.