Greetings.
Tire size will influence many decisions in your build. If you want to go 33" tires a 4" lift will not suffice with out some 'fender trimming'. You will also find that the 33" tires with your stock axle gears will make the acceleration a bit sluggish, especially if you have the taller stock gears and not the 3.31 gears that came on some of rigs.
Spring lifts tend to provide a bit harsher ride compared to stock but most people find a 4" spring lift to be acceptable in terms of comfort and drivability. With a 4" spring only lift you can fit 31" tires without trimming the fenders and with minimum rubbing. Here's my old waggy sporting a 4" rusty lift and 31" tires:
My truck came with the 3.31 axle gears and with the 31" tires the acceleration was acceptable.
If you want bigger tires and no fender trimming then you are looking at a 6" lift. There are 6" 'spring only' lifts available but the ride become harsher and articulation suffers a bit. This is because the springs have a lot of arch to them in order to provide the extra lift. If you look at your waggy you will see the springs are 'flat'. A lift kit will provide springs with an arch large enough to raise the jeep up.
Your friends suggestion of a 'front over axle' is a popular option. It is typically referred to as a 'Spring Over Axle' or 'SOA'. I clarify this for you so if you do searching on options you will get more 'hits'. If you look at the front suspension of your waggy you will see the front springs attach to the front axle on the bottom. What a SOA does is place the springs on top of the axle. It is good for 6 plus inches of lift. There is nothing inherently wrong with placing the springs on top of the axle, many other stock trucks came with this configuration. If you go this route there are some steering component changes that must me done. Searching SOA on this board will provide a lot of info on the changes required. 'Generally' an SOA conversion will provide a smoother ride and more articulation when compared to a 6" spring only lift because you can keep the springs relatively flat. My Cherokee has a SOA conversion and I like the ride very much.
Your friend also suggested blocks in the back. If you look at the rear axle you will see that, unlike the front axle, the springs already sit on top of the axle. It is 'easy' to add lift by simply placing a block in between the spring and the axle. A 2" block will add 2" of lift, 4" will add 4" of lift and so on. Adding blocks to the rear axle is one of the great debates in the off road community. Some people will say 'never do it' others will argue that it is fine. Everyone agrees that if you do it, get good quality blocks. The compromise that blocks cause is they will cause greater torque against the spring compared to no blocks. When you accelerate your tires apply force against the rear axle and try to rotate it. The springs counteract this force. The same happens when you brake, the axle is trying to rotate and the springs counteract the rotation. When you place a block in between the axle and the spring the amount of force on the spring is multiplied. The taller the block the greater the multiplication. This means the axle will rotate more during acceleration and braking and the spring will 'bend' more as a result. This extra force is stored in the spring and then released as it returns to its normal state. This can cause wheel 'hopping'. How much hopping? It depends on the size of the block and the stiffness of the springs. Wheel hop is bad, especially in braking, because it reduces overall control. All that being said, and there is much more on the subject available, a 6" block with your stock springs on the rear axle would not be recommended by most people and, in my case, I would discourage the use of blocks in your situation.
But all is not lost. Another option for gaining 6" or so of lift without adding new springs or blocks to the rear axle is called a 'shackle flip'. I've already written too much so I won't go into details but basically a shackle flip reorients how the springs are attached to the frame. It is the recommended solution for adding rear lift when doing an SOA in the front. If you search 'shackle flip' you will find lots of info on how to do this.
Have you seen other lifted rigs in person? What is your motivation for lifting your rig?
I am not talking you out of a BJ's lift but I would suggest you delay the decision and do a bit more research on the positives/negatives of lifting a rig and how the lift is done. Also, if you haven't seen lifted rigs in person try to hook up with some of the folks on the board and elsewhere. You might find you like the stance of a 4" lift with 31" tires over a 6" lift with 33" tires.
I hope this helped!