Something like this should work. Very similar to your existing code.
The exact syntax of the filter might have to be changed.
private void buttonSearch_Click(object sender, EventArgs e)
{
table1BindingSource.Filter = string.Format("([{0}] >= {1} AND [{0}] <= {2})", "Size", Textbox1.Text, Textbox2.Text);
}
For help with the syntax see
DataColumn.Expression Property[
^]