If you think you are going to photograph a field of diagonal about 6" or 150mm: that is a magnification of about m = 1:4 on 35mm, and 1:2 on 6x6.
You will have a lens to subject distance of about d_object = f * (1 + 1/m), so for "normal" focal length lenses of 50mm and 80mm, that's about 250mm and 240mm respectively. IOW if you use normal length lenses on both formats, the lens to subject distance doesn't change much, which makes sense since they both have "normal" angles of view.
If you use longer-than-normal focal length lenses, you gain more working distance, but you need a lot of extension (focus travel or bellows).
I think this distance is about at the close limit of Rolleinars, and attainable with a Mamiya C with the 80mm lens, but not with the longer lenses like 135 or 180mm. Attached is a table from a Mamiya C manual that shows the minimum field size achievable with each lens.
For close ups of people (body art?) where you have a 3-d, not perfectly still, subject and are hand holding, I'd really be concerned about speed of operation and of parallax error in focusing, that is focusing on some spot that isn't quite where the taking lens is pointed.
I understand the desire not to buy more stuff than one needs, but there are good reasons why people use SLRs for close up work. I think either a parallax compensated close up like the Rolleinar, or an SLR with a normal lens + close up, or an actual macro lens, is indicated. If you did look at medium format SLRs, they unfortunately aren't cheap any more, but MF macro lenses are often surprisingly not overpriced (I suppose they are in less demand from the "must have fast lenses for blur" users).