BHK-21 cells are the most sturdy cells i ever used. we use BHK-21 cells with SIGMA MEM +10%FCS and 5% TPB(Tryptose phosphate broth. If u properly maintan the seeding conecntration of .25 million cells per ml u will not face any problem. As far as mycoplasma contamination is concern it firstly slower down the cell growth rather than killing them and u will have bird's eye appearance in culture.
I think you are facing the problem because of over trypsinisation.