There are many used E flat tubas around collecting dust. With a little repair, the instrument will play well. The E flat has the added advantage of playing the high register more easily. It is important to note that for many years the band repertoire used both the BB flat and E flat in fifths and octaves with splendid results. Trumpet players may also go directly to BB flat tuba, but it will be more difficult getting used to the new instrument size, low pitch, and a new clef to read.
Many performance problems are a result of bad posture.
The student should sit up straight and hold the chin up so the throat is unrestricted. Students should not lean back into the chair. The student should sit on the end of a the chair with their thighs in a slightly downward angle. This allows for quick, unrestricted deep breaths. In many cases a stand would be very helpful.