How to make a flexible list layout with an anchored button in Flutter?

I'm building a polling form, in which the user specifies a question and a flexible number of choices. There is a "Send" button at the bottom.

However, I run into issues when interacting with the form. Adding too many choices causes the ListView to draw underneath the Send button. Tapping on a textfield in the lower half of the screen results in the selected field being obscured by the keyboard and Send button. Here is the code:

@override
  Widget build(BuildContext context) {
     return Scaffold(
        //resizeToAvoidBottomPadding: false, // keyboard will cover floating elements
        appBar: AppBar(title: Text('Add Question')),
        body: Container(
           padding: EdgeInsets.symmetric(horizontal: 16.0, vertical: 24.0),
           child: Column(
              mainAxisAlignment: MainAxisAlignment.start,
              children: <Widget>[
                 Expanded(
                    child: ListView(
                       //crossAxisAlignment: CrossAxisAlignment.stretch,
                       children: <Widget>[
                          TextFormField(
                             decoration: InputDecoration(labelText: 'Question'),
                             initialValue: _questionText,
                             validator: (value) {
                                if (value.isEmpty) {
                                   return 'Please enter some text';
                                }
                             },
                          ),
                          SizedBox(height: 16.0),
                          Center(
                             child: Text('Choices'),
                          ),
                          SizedBox(height: 16.0),

                          buildForm(),

                          SizedBox(height: 16.0),
                          RaisedButton.icon(
                             icon: Icon(Icons.add),
                             label: Text('Add Choice'),
                             onPressed: () {
                                final x = _questionChoices.length;
                                _addChoice("Test $x");
                             },
                          ),
                          SizedBox(height: 16.0),
                       ],
                    ),
                 ),
                 RaisedButton(
                    child: Text('SEND QUESTION'),
                    onPressed: () {
                       _sendQuestion();
                    },
                 )
              ],
           ),
        ),
     );
  }

  Widget buildForm() {
     List<Widget> list = new List();
     for (var index = 0; index < _questionChoices.length; index++) {
        list.add(Row(
           crossAxisAlignment: CrossAxisAlignment.center,
           children: <Widget>[
              IconButton(
                 icon: Icon(Icons.remove_circle),
                 color: Colors.deepOrange,
                 tooltip: 'Remove Choice',
                 onPressed: () {
                    _removeChoice(index);
                 },
              ),
              Flexible(
                 child: TextFormField(
                    decoration: InputDecoration(hintText: 'Enter choice text.'),
                    initialValue: _questionChoices[index],
                    validator: (val) {
                       val.length == 0 ? 'Please enter a value.' : null;
                    },
                    onSaved: (val) => _questionChoices[index] = val,
                 ))
           ],
        ));
        list.add(SizedBox(
           height: 12.0,
        ));
     }
     return Column(children: list);
  }