Being tuned in fourths, as long as you (no not completely, but) somewhat avoid open strings, anything you play anywhere can be moved anywhere else on the neck and played in any key.
If you are a smaller person smaller hands, there are short neck basses that are more the length of a regular six string electric guitar, and even in first position a small hand can play one finger per fret, rather than feeling compelled to use string bass left hand technique.
Find someone to help you find an inexpensive bass with decent electronics and a nice straight neck. Anything else is like trying to play a broken tuba. The same goes for amplification. Often, 60 watts with a good sounding speaker is plenty of sound. Just as with tubas, it's risky to buy mail order from pictures, because even expensive basses sometimes have crappy necks which can't be straightened and issues with used amplifiers don't need to be expounded upon because those are already understood by everyone reading this. I can't emphasize enough how much work it is to play a bass guitar with a crappy neck. Think of a tuba with sticky valves that can't be repaired.
There are so many places online ($0.00) that can show beginners how to get started and how to advance. It seems as though - for every pop song ever written - there's a YouTube video with someone demonstrating in detail how to play the prominent licks.
Being frank, if we individually don't sport this weakness, we know that tuba players as a group are the weakest of all brass players as far as reading or aurally dissecting complicated and/or funky rhythms. Playing pop music on the bass puts you right there in the midst of these rhythms. Of course, if playing jazz, a bass player is going to be expected to be able to play in 4/4 and - once someone begins to master this on the bass - they can transfer it to the tuba. The nice thing about doing most anything on a bass guitar is that it's all right there in front of your face and all the intervals can be visually interpreted (not that I recommend staring at the neck, as that becomes a crutch, and also doesn't look very good - amateurish? - on stage... Moreover, it's the same sort of hindrance as relying on staring at the keyboard when typing. Finally, if a bass guitar job involves reading music - whether notes on the staff, chord changes and slashes, or whatever - how in the world is a bass player going to be able to keep their place by staring at the neck 90% of the time and only glancing at the music 10% of the time? Yeah. The neck of a guitar needs to be as familiar as the slide is to a trombonist. That said, trombonists get to look at their slides, don't they?
) Significantly and importantly, I believe that playing the electric bass (and playing the upright bass is wonderful, but the bass guitar is just so much more accessible to someone who has never played either) helps to pull tuba players away from defining their "music" as pieces of paper with lines and dots on them, and pulls them more towards being rounded musicians (whereby the music is inside ~themselves~, rather than thinking of "music" as pieces of paper). Again, this is possible to do with the tuba, but doing this on the bass guitar offers an easy bridge to doing this on the tuba - at least, that's the way it worked for me.
There are lots of bass guitars out there that are ready to go (maybe even with okay strings on them sometimes) used for under $200, and the same goes for amplifiers which have just enough power to use on stage, so realize that a person can outfit themselves (with carefully chosen used equipment) for about the same price as some tuba bags, mutes, and other tuba accessories. I've seen other boutique tuba mouthpieces that cost more, but were someone to choose every single add-on offered as options with my three-piece stainless steel mouthpieces, a mouthpiece can end up costing $300
... and I've seen some pretty decent a-bit-better-than-entry-level used basses in pawn shops for about that amount of money, occasionally.I'm not just recommending this for amateur players. I'm actually recommending this for working professional tuba players and very serious tuba students who might even be enrolled in conservatories. For those who embrace the (voodoo?) about "you shouldn't play a different mouthpiece other than the one that you normally use", well... (with bass guitar) no mouthpiece.
Again, it really tends to widen a tuba-only player's definition of "music", expands the brain's ability to understand and interpret music (perhaps benefits unknown to me as well?), and I believe it can also improve one's TUBA playing, as this instrument is the same voice as the tuba, but simply played in a completely different way.
I hadn't played bass guitar for several decades, and - just this last year or so - have been roped back into it. I'm really glad. I forgot about how much pleasure it brought to me.
) 
it's a very good instrument, but this is not what I Guild is known for.