insulation for 66 Marlette-need company info/specs

[Theresa Bonneau]

I'd like to get info on the safest, most effective way to increase the heat-holding potential of my 66 Marlette. I've heard of blown-in sawdust (didn't work well, burst through top), foam insulation(?, $?), what other solutions to increase heat retention in winter? thanks, TB in E. Hartford CT