Respirators aren't nearly as important as eye protection and welder's apron and gloves. It's very hard to get much lead airborne at casting temperatures. Primer dust from case cleaning tumblers is much more hazardous. Use good ventilation to get the flux smoke carried off, and you'll be fine.
I bought one of the Lee tumble lube molds for .38 wadcutters and got the most accurate wadcutters I've ever shot. I got their
6-cavity mold, and consider that worth the cost because it makes production so much faster. Nonetheless, you can get the very inexpensive
2-cavity version to try it out. The tumble lube bullets are not only good shooters, they save you having to invest in lubricating and sizing equipment as they are normally fired at as-cast diameter and are lubed with Lee Liquid Alox lube.