Go Patagonia is a small Punta Arenas agency registered with SERNATUR specifically under excursionismo o trekking, which in Chile is a separate adventure-tourism licence from the general tour-operator one and requires the safety documentation that goes with it. If you want someone to walk with in Magallanes rather than a seat on a bus, this is the category to look for.
They are on Lautaro Navarro, two blocks from the plaza, in the row of agency offices that also holds WhaleSound and Fiordos del Sur. Prices are quoted rather than listed.
Contact is unusually well signposted: a landline, two mobiles, three email addresses and a WhatsApp button on every page whose number matches both the mobile they print and the one on their SERNATUR registration.