As far as there are ever hard-and-fast rules in writing (which there aren't!) you should avoid switching tense within a paragraph or even scene unless the change is consistent. Just as you should avoid changing person mid paragraph or section.
Any change that jars the reader pulls them out of the story. And any time a reader is pulled out there is a chance they won't bother to go back in.
As an example; in a scene in Fallen Dragon by Peter F. Hamilton, there is a scene where he changes person and time mid-section. He goes from a soldier walking up a beach being pelted with stones as he walks through the town, to a woman watching the soldier begin to emerge from the water and gathering stones to start throwing.
If the change is consistent it can be handled, particularly if it is clear why the change is happening, but if the change just happens it will be impossible for the reader to become accustomed to it. Every time I hit a change like this, whether it’s time, tense, person or even a consistency fail — a pipe becoming a cigar because the writer forgot the character was smoking a pipe — I’m thrown out of the world and back into my chair while I try to figure out what just happened.
Peter F. Hamilton’s one of my favourite authors, despite his faults, and I give him time and allowances I would not give an author I was reading for the first time.
Regarding your example specifically:
I now also wanted to get to know...
now in this context doesn't have to be a tense change, it can still be used in past tense, and simply adds a sense of immediacy to the moment without changing tense. On the other hand...
My guess is that it...
This one is definitely present tense and is a sudden and jarring change. The edits that Aibrean suggests would be ideal.