Wedding flowers for the church don't have to be too fussy. Personally if we were getting married in a church, we would have a bouquet or two on the altar for my decorations and big bows of satin or tulle on the pews. This would save you a lot of grief because they could be damaged if water leaked on the pews or if they were scratched with wire.
Check with your church anyway and see what their policy is on adornments and blooms. You could use a few pretty silk flowers and you wouldn't have to worry about water. Make a large bow with a loop of ribbon on the back. Put a few silk flowers in the bow and hang around the pew. This is a beautiful way to have wedding flowers for the church.
If you're lucky there may be church flowers already there and you can just use those.
If you are having a garden wedding there may be an arch or a trellis involved. The easy way to decorate an arch is with artificial flowers attached to the arch with plastic cable ties purchased at your hardware store.
It's easy because you don't have to worry about keeping them alive and they can be done the day before. Just arrange in a fashion that hides the plastic ties. Use flowers that are the same type that you are using in your wedding. You may use tulle or ribbon in conjunction with the flowers.
A trellis can be decorated pretty much the same as an arch. Just weave some tulle through the trellis and attach some flowers. Pick silk flowers that look as real as possible. There are some beautiful ones out there.
Church flowers, arrangements, an arch or a trellis really don't need a lot of blooms if you use some pretty trailing greens such as ivy. They go a long way.