How about spray foam?

If you stick with batts, don't forget the need to have a vapor barrier.

The R49 batts are heavy, so I would think you would have to space the 1 X4 lumber 12 - 16 inches apart. Maybe it would be easier to install perpendicular 4 X 8 sheets of plywood. You could use the least expensive plywood you can find. You could install a sheet, then install the insulation above it. Repeat the process until the entire ceiling is covered.

If you have ceiling joists an easier, cheaper way than two by fours or plywood is tie wire. Just make sure you properly support the batts. either three wires or z pattern under every four feet of batt attached to your trusses.

To mojavemaria - to be sure I understand: you are suggesting a z pattern on the underside of the ceiling joists so the batts can be laid within the cavity between the joists? That makes good sense and seem very economical.