Ultracold atomic mixtures offer a multitude of opportunities for addressing few-body physics. In recent experiments we have investigated mixtures of K and Rb as well as spin mixtures of K. These mixtures are produced by exploiting a total of three Feshbach resonances for simultaneous tuning of the 39K intraspecies and the 39K-87Rb interspecies scattering lengths [1]. Our investigation of Efimov physics was triggered by an unexpected non-universal behavior of E_mov resonances across isotope combinations in K+Rb . I will present our measurements of the scattering length dependent threebody recombination coefficient in heteronuclear mixtures of 39K-87Rb and 41K-87Rb, which do not show any signatures of Efimov resonances [2]. In more recent experiments we have therefore investigated homonuclear Efimov resonances in 39K with the aim of observing multiple Efimov resonances on adjacent Feshbach resonances. This has led to the observation of an unexpected temperature dependence of the Efimov resonance strength, which remains to be understood. I will present and discuss recent experimental data. In the second part of the talk I will discuss the use of two spin components of 39K to investigate the Bose polaron [3]. Radio frequency spectroscopy between the two components shows the existence of a well-defined quasiparticle state for an impurity interacting with the BEC and allows for a measurement of its energy for attractive and repulsive interactions. Our results show that the spectral response consists of a well-defined quasiparticle peak at weak coupling which is strongly broadened for increasing interaction strengths. This opens up intriguing prospects for studying mobile impurities in a bosonic environment, as well as strongly interacting Bose systems in genera