Hi Mightyh,
I would always measure to make sure that any support system fits inside your bedframe (they provide the exact dimensions on the site) and you will also need to make sure that there is a way to secure the slats to the frame so that they don’t shift or fall through the frame. If you confirm they will fit and they can be attached securely then douglas fir is a strong wood and you would be fine with either one of the gap sizes as long as the bedframe itself is strong enough to support the weight of the mattress and anyone that sleeps on it.
I haven’t talked with them and don’t know them personally but they certainly appear to be reputable to me.
@PC gal,
Brooklyn Bedding is a completely transparent manufacturer and lists the materials in their mattresses on their website (and will answer any specific questions that their customers have as well) so that all their customers can know exactly what is inside any mattress that they purchase from them.
As you can see here … the slats in your foundation may be a little too far apart to be the best choice for an all latex mattress without an extra set of slats.
Phoenix